D

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

#define ll long long
#define nl "\n"

void files(){
    ios_base::sync_with_stdio(false),cin.tie(NULL),cout.tie(NULL);
    #ifndef ONLINE_JUDGE
        freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
    #endif
}


void solve(){
    ll a,b,c,d; cin>>a>>b>>c>>d;
    if(a > b) swap(a,b);

    ll ans = b/c - (a-1)/c + b/d - (a-1)/d - b/(c*d) + (a-1)/(c*d);
    cout<<b-a+1-ans<<nl;

}

int main(){
    files();
    int t = 1;
    // cin>>t;
    while(t--) solve();

    return 0;
}