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

long long a,b,x,y,z,dem[5];

int main()
{
    freopen("COUNTNUM.inp","r",stdin);
    freopen("COUNTNUM.out","w",stdout);
    cin>>a>>b>>x>>y;

    z=(x*y)/__gcd(x,y);

    if(a%x==0) dem[1]=b/x-a/x+1;
    else dem[1]=b/x-a/x;
    if(a%y==0) dem[2]=b/y-a/y+1;
    else dem[2]=b/y-a/y;
    if(a%z==0) dem[3]=b/z-a/z+1;
    else dem[3]=b/z-a/z;
    cout<<(b-a+1)-(dem[1]+dem[2]-dem[3]);
}