#pragma GCC optimize("02,unroll-loops")
#include <vector>
#include <iostream>
// #include <cassert>
#include <algorithm>
#define all(x) begin(x), end(x)
using namespace std;
const int N = 1e5 + 5;
const int K = 51;
const int inf = 1e9;
int dp[3][K][K][3]; // i, 0: [a][b], 1: [a][c], 2: [b][c]
int ci, pi, ni;
int n, k;
void rm(int i, int a, int b, int c, int pre) {
// assert(a > 0 && b > 0 && c > 0);
if (a == 1) {
int m = 2; // [b][c]
// chmax(dp[b-1][c-1][m], pre + 1);
dp[ci][b-1][c-1][m] = max(dp[ci][b-1][c-1][m], pre + 1);
}
if (b == 1) {
int m = 1; // [a][c]
// chmax(dp[a-1][c-1][m], pre + 1);
dp[ci][a-1][c-1][m] = max(dp[ci][a-1][c-1][m], pre + 1);
}
if (c == 1) {
int m = 0; // [a][b]
// chmax(dp[a-1][b-1][m], pre + 1);
dp[ci][a-1][b-1][m] = max(dp[ci][a-1][b-1][m], pre + 1);
}
}
void m0(int i, int a, int b, char ch) {
int m = 0; // [a][b]
int pre = dp[pi][a][b][m];
if (pre < 0)return; // previous state impossible
// always: (not taking current character)
// chmax(dp[a][b][m], pre);
dp[ci][a][b][m] = max(dp[ci][a][b][m], pre);
if (a + b == k) return; // can't take current character
if (ch == 'A') {
// chmax(dp[a+1][b][m], pre);
dp[ci][a+1][b][m] = max(dp[ci][a+1][b][m], pre);
return;
}
if (ch == 'B') {
// chmax(dp[a][b+1][m], pre);
dp[ci][a][b+1][m] = max(dp[ci][a][b+1][m], pre);
return;
}
// else ch == 'C'
int c = 1;
int mn = min({a, b, c});
if (mn > 0) {
rm(i, a, b, c, pre); // try removing different stuff
return;
}
// now either a == 0 or b == 0
// assert(a == 0 || b == 0);
if (a == 0) {
m = 2; // [b][c]
// chmax(dp[b][c][m], pre);
dp[ci][b][c][m] = max(dp[ci][b][c][m], pre);
}
if (b == 0) {
m = 1; // [a][c]
// chmax(dp[a][c][m], pre);
dp[ci][a][c][m] = max(dp[ci][a][c][m], pre);
}
}
void m1(int i, int a, int c, char ch) {
int m = 1; // [a][c]
int pre = dp[pi][a][c][m];
if (pre < 0)return; // previous state impossible
// always: (not taking current character)
// chmax(dp[a][c][m], pre);
dp[ci][a][c][m] = max(dp[ci][a][c][m], pre);
if (a + c == k) return; // can't take current character
if (ch == 'A') {
// chmax(dp[a+1][c][m], pre);
dp[ci][a+1][c][m] = max(dp[ci][a+1][c][m], pre);
return;
}
if (ch == 'C') {
// chmax(dp[a][c+1][m], pre);
dp[ci][a][c+1][m] = max(dp[ci][a][c+1][m], pre);
return;
}
// else ch == 'B'
int b = 1;
int mn = min({a, b, c});
if (mn > 0) {
rm(i, a, b, c, pre); // try removing different stuff
return;
}
// now either a == 0 or c == 0
// assert(a == 0 || c == 0);
if (a == 0) {
m = 2; // [b][c]
// chmax(dp[b][c][m], pre);
dp[ci][b][c][m] = max(dp[ci][b][c][m], pre);
}
if (c == 0) {
m = 0; // [a][b]
// chmax(dp[a][b][m], pre);
dp[ci][a][b][m] = max(dp[ci][a][b][m], pre);
}
}
void m2(int i, int b, int c, char ch) {
int m = 2; // [b][c]
int pre = dp[pi][b][c][m];
if (pre < 0)return; // previous state impossible
// always: (not taking current character)
// chmax(dp[b][c][m], pre);
dp[ci][b][c][m] = max(dp[ci][b][c][m], pre);
if (b + c == k) return; // can't take current character
if (ch == 'B') {
// chmax(dp[b+1][c][m], pre);
dp[ci][b+1][c][m] = max(dp[ci][b+1][c][m], pre);
return;
}
if (ch == 'C') {
// chmax(dp[b][c+1][m], pre);
dp[ci][b][c+1][m] = max(dp[ci][b][c+1][m], pre);
return;
}
// else ch == 'A'
int a = 1;
int mn = min({a, b, c});
if (mn > 0) {
rm(i, a, b, c, pre); // try removing different stuff
return;
}
// now either b == 0 or c == 0
// assert(b == 0 || c == 0);
if (b == 0) {
m = 1; // [a][c]
// chmax(dp[a][c][m], pre);
dp[ci][a][c][m] = max(dp[ci][a][c][m], pre);
}
if (c == 0) {
m = 0; // [a][b]
// chmax(dp[a][b][m], pre);
dp[ci][a][b][m] = max(dp[ci][a][b][m], pre);
}
}
// void fill_with_inf(vector<vector<vector<int>>>& x) {
// for (int a = 0; a <= k; ++a) {
// for (int b = 0; a + b <= k; ++b) {
// for (int m = 0; m < 3; ++m) {
// x[a][b][m] = -inf;
// }
// }
// }
// }
int main() {
cin.tie(0)->sync_with_stdio(0);
cin >> n >> k;
string s; cin >> s;
s = "#" + s;
// fill_with_inf(pre_dp);
// fill_with_inf(dp);
// fill_with_inf(new_dp);
// pre_dp[0][0][0] = pre_dp[0][0][1] = pre_dp[0][0][2] = 0;
//
pi = 0, ci = 1, ni = 2;
for (int i = 0; i < 3; ++i) {
for (int a = 0; a <= k; ++a) {
for (int b = 0; a + b <= k; ++b) {
for (int m = 0; m < 3; ++m) {
dp[i][a][b][m] = -inf;
}
}
}
}
dp[pi][0][0][0] = dp[pi][0][0][1] = dp[pi][0][0][2] = 0;
int ans = 0;
for (int i = 1; i <= n; ++i) {
char ch = s[i];
for (int e = 0; e <= k; ++e) {
for (int f = 0; e + f <= k; ++f) {
for (int m = 0; m < 3; ++m) {
m0(i, e, f, ch);
m1(i, e, f, ch);
m2(i, e, f, ch);
}
}
}
pi = (pi + 1) % 3;
ci = (ci + 1) % 3;
ni = (ni + 1) % 3;
// swap(pre_dp, dp);
// swap(dp, new_dp);
}
for (int a = 0; a <= k; ++a) {
for (int b = 0; a + b <= k; ++b) {
for (int m = 0; m < 3; ++m) {
// chmax(ans, pre_dp[a][b][m]);
ans = max(ans, dp[pi][a][b][m]);
}
}
}
cout << ans << "\n";
}
