Book writing

#include <iostream>

using namespace std;
long pow(long b, long p, long mod) {
    if (p == 1) return b%mod;
    if (p == 0) return 1%mod;
    if (p%2 == 0) {
        long t = pow(b, p/2, mod);
        return (t*t)%mod;
    } else return (pow(b, p-1, mod)*b)%mod;
}
int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    long a, b;
    cin >> a >> b;
    cout << pow(3, a-1, b) << endl;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED