Finding inverse

#include <bits/stdc++.h>
using namespace std;
#define rep(i, a, b) for(int i=a;i<(b);++i)
#define all(x) begin(x),end(x)
#define sz(x) int((x).size())
using ll = long long;
using pii = pair<int,int>;
using vi = vector<int>;
using ld = long double;

int M = 1e9+7;

int mpow(ll a, ll p) {
  ll r = 1;
  while (p != 0) {
    if (p & 1) {
      r *= a; r %= M;
    }
    a *= a; a %= M;
    p >>= 1;
  }
  return r;
}

int main() {
  int a;
  cin >> a >> M;
  int r = mpow(a,M-2);
  if (ll(a) * r % M != 1) cout << "-1\n";
  else cout << r << '\n';
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: WRONG ANSWER

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: WRONG ANSWER

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: WRONG ANSWER

Test 11

Verdict: ACCEPTED

Test 12

Verdict: WRONG ANSWER

Test 13

Verdict: WRONG ANSWER

Test 14

Verdict: ACCEPTED