#include<bits/stdc++.h>
using namespace std;
long long a, b, c, d,t=0,x,y,k,z;
int main() {
     cin >> a >> b >> c >> d;
    ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
    freopen("countnum.inp","r",stdin);
    freopen("countnum.out","w",stdout);
     x = b / c - (a - 1) / c;
     y = b / d - (a - 1) / d;
     k = (c * d) / __gcd(c, d);
     z = b / k - (a - 1) / k;
     t= b - a + 1 - x - y + z;
   cout << t;
}