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