#include<bits/stdc++.h>
#define endl '\n'
#define int long long
#define And << " " <<
#define reset(a, x) memset(a, x, sizeof(a))
#define FOR(i, l, r) for (int i = l; i <= r; i++)
#define fast() ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
using namespace std;

const int N = 1e2 + 5;


int lcm(int a, int b) {
    return (a / __gcd(a, b)) * b;
}

int32_t main()
{
    fast();
    freopen("countnum", "r", stdin);
    freopen("countnum", "w", stdout);
    int l, r, a, b;
    cin >> l >> r >> a >> b;
    int t = lcm(a, b);

    int c = (r / a) - ((l-1) / a);
    int d = (r / b) - ((l-1) / b);

    int e = (r / t) - ((l-1) / t);

    cout << (r-l+1) - (c + d - e);
    cout << '\n' << "\n"; return 0;
}
//2 14 3 8