Finding inverse

#include <bits/stdc++.h>
using namespace std;

#define I_2D(row, col, width) ((row) * (width) + (col))
#define PRINT_ARR(arr, n)                                                      \
  do {                                                                         \
    for (int i = 0; i < n; i++) {                                              \
      cout << arr[i] << " ";                                                   \
    }                                                                          \
    cout << "\n";                                                              \
  } while (0)
#define PRINT_VEC_ARR(v, n)                                                    \
  do {                                                                         \
    for (int i = 0; i < n; i++) {                                              \
      cout << i << ": ";                                                       \
      for (auto item : v[i]) {                                                 \
        cout << item << " ";                                                   \
      }                                                                        \
      cout << endl;                                                            \
    }                                                                          \
  } while (0)
#define endl '\n';

typedef long long ll;

ll _gcd(ll a, ll b) {
  if (b < 1) {
    return a;
  }
  return _gcd(b, a % b);
}

ll modpow(ll a, ll b, ll m) {
  // a^b % m
  ll res = (b & 1) ? a : 1;
  b >>= 1;
  for (; b; b >>= 1) {
    a = (a * a) % m;
    if (b & 1) {
      res = (res * a) % m;
    }
  }
  return res;
}

ll euler_totient_fnc(ll n) {
  ll res = 1;
  for (ll i = 2; i * i <= n; i++) {
    ll curr = 1;
    ll count = -1;
    while (n % i == 0) {
      count++;
      if (count > 0) {
        curr *= i;
      }
      n /= i;
    }
    if (count >= 0) {
      curr *= (i - 1);
    }
    res *= curr;
  }

  if (n > 1) {
    res *= n - 1;
  }
  return res;
}

ll inverse_modulo(ll a, ll m) {
  ll euler_totient = euler_totient_fnc(m) - 1;
  return modpow(a, euler_totient, m);
}

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  ll a, m;
  cin >> a >> m;
  if (_gcd(a, m) != 1) {
    cout << -1 << endl;
    return 0;
  }

  cout << inverse_modulo(a, m) << endl;
  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