Finding inverse

#include <bits/stdc++.h>

using namespace std;

//Definitions for quicker writing
#define REP(i,a,b) for (int i = a; i < b; i++)
#define clz __builtin_clz
#define ctz __builtin_ctz
#define popct __builtin_popcount
#define PB push_back
#define MP make_pair
#define F first
#define S second
#define X real()
#define Y imag()

//Typedefs for quicker writing
typedef long long ll;
typedef vector<int> vi;
typedef vector<long long> vl;
typedef pair<int,int> pi;
typedef pair<long long, long long> pl;
typedef complex<long long> po;

//Max values
const long long lmx = LLONG_MAX;
const int imx = INT_MAX;

ll modpow(ll x, ll n, ll m) {
    if (n == 0) return 1%m;
    ll u = modpow(x,n/2,m);
    u = (u*u)%m;
    if (n%2 == 1) u = (u*x)%m;
    return u;
}

ll gcd(ll a, ll b){
    if(b==0) return a;
    return gcd(b,a%b);
}

ll totient(ll n){
    ll res = n;
    for(ll i=2; i*i <= n; i++){
        if(n%i == 0){
            while(n%i == 0){
                n /= i;
            }
            res -= res/i;
        }
    }

    if(n>1) res -= res/n;

    return res;
}

int main() {
	//IO optimization
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	//Input definition
	ll a,m;

	//Read In
	cin >> a >> m;

	//Main part
    ll res;
    if(a==0 || m == 0){
        res = -1;
    }
    else{
       if(gcd(a,m) != 1){
           res = -1;
       }
       else{
           ll tot = totient(m);
           res = modpow(a, tot-1, m);
       }
    }

	//Write out
	cout << res << "\n";
		
	//Return
	return 0;

}

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