#include<bits/stdc++.h>
using namespace std;
long long bc(long long a,long long b)
{
   return (a*b)/__gcd(a,b);
}

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 c=R-L+1;
    long long x=R/a-(L-1)/a;
    long long y=R/b-(L-1)/b;
    long long z=R/bc(a,b)-(L-1)/bc(a,b);
    cout<<c-(x+y-z);
}