#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;
}
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