#include <bits/stdc++.h>
typedef long long ll;
#define FOR(i,l,r) for (int i=l;i<=r;i++)
#define FOD(i,r,l) for (int i=r;i>=l;i--)
#define fast ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);

using namespace std;
int BCNN(int a, int b)
{
    int result = __gcd(a, b);
    return a * b / result;
}
int main()
{
    freopen("countnum.inp","r",stdin);
    freopen("countnum.out","w",stdout);
    fast;
    ll L,R,a,b; cin>>L>>R>>a>>b;
    int t = BCNN(a,b);
    ll s, sa , sb, sab;
    s = R - L + 1;
    sa = s/a;
    sb = s/b;
    sab = (R / t) - ((L-1) / t);
    cout<< s - (sa + sb - sab);
}