#include<bits/stdc++.h>

using namespace std;

long long a, b, c, d,t=0;

int main() {
    freopen("countnum.inp","r",stdin);
    freopen("countnum.out","w",stdout);
   
    cin >> a >> b >> c >> d;
    for (long long i = a; i <= b; i++) {
        if (i % c != 0 && i % d != 0) {
            t++;
        }
    }
  
    cout << t;
  
    return 0;
}