#include <iostream>
#include <cstdlib>

long modinv(long src, long mod)
{
    long num = mod - 2;
    long res = 1;
    while(0 < num){
        if(num % 2 == 1){
            res = (res * src) % mod;
            num--;
        }
        src = (src * src) % mod;
        num /= 2;
    }
    return res;
}

int main()
{
    long a, b, c, d;
    std::cin >> a >> b >> c >> d;
    a *= b; a %= d;
    a *= modinv(c, d); a %= d;
    std::cout << a << std::endl;
}