#include<bits/stdc++.h>
using namespace std;

int main()
{
    freopen("countnum.inp", "r", stdin);
    freopen("countnum.out", "w", stdout);
    long long L,R,a,b;
    cin>>L>>R>>a>>b;

    long long T = R - L + 1;
    long long A = R/a - (L-1)/a;
    long long B = R/b - (L-1)/b;
    long long C = (a*b) / __gcd(a,b);
    long long D = R/C - (L-1)/C;

    cout<< T - A - B + D;
    return 0;
}