фцв

#include <bits/stdc++.h>

using namespace std;
using ll = long long;

int binpow (int a, int n) {
    if (n == 0)
        return 1;
    if (n % 2 == 1)
        return binpow (a, n-1) * a;
    else {
        int b = binpow (a, n/2);
        return b * b;
    }
}

int main() {
    int a, b, n, m;

    cin >> a >> b >> n >> m;

    int t = (((b - a) * binpow(n, m - 2)) % m + m) % m;
    cout << a + t * n;
    return 0;
}