#include <bits/stdc++.h>   using namespace std;   long mk[100000];   int main() {     long a, b, m, r0, r;     cin >> a >> b >> m >> r0;     for (long i = 0; i < m; i++) mk[i] = -1;     r = (a * r0 + b) % m;     mk[r] = 1;     long k = 1;     while (true) {       k++;       r = (a * r + b) % m;       if (mk[r] == -1)         mk[r] = k;       else {         cout << k - mk[r];         return 0;       }     }     return 0;   }   