#include <bits/stdc++.h>
#define fi first
#define se second
#define bit(x) (1LL << (x))
#define getbit(x, i) (((x) >> (i)) & 1)
#define ALL(x) (x.begin(), x.end())
using namespace std;

template <typename T1, typename T2> bool maxi(T1 &a, T2 b) {
    if (a < b) {a = b; return true;} return false;
}

template <typename T1, typename T2> bool mini(T1 &a, T2 b) {
    if (a > b) {a = b; return true;} return false;
}

const int N = 2e5 + 5;
const int oo = 1e9;
const long long ooo = 1e18;


int main() {
    int a, b;
    int c, d;
    cin >> a >> b >> c >> d;
    int lcm = b/__gcd(b,d)*d;
    cout << lcm-max(a,c) << "\n";
}