#include "bits/stdc++.h"
using namespace std;
#define ll long long
#define endl '\n'
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define rep2(i,a,b) for(int i=int(a);i<int(b);i++)
#define pb emplace_back
#define all(x) (x).begin(),(x).end()
ll mod=1e9+7;
ll mod2=998244353;
const int INF=1e9;

unsigned euclidean_gcd(unsigned a, unsigned b) {
	if(a < b) return euclidean_gcd(b, a);
	unsigned r;
	while ((r=a%b)) {
		a = b;
		b = r;
	}
	return b;
}

signed main() {
	ll a,b,c,d;
	cin>>a>>b>>c>>d;
	ll ans=b/c+b/d;
	a--;
	ll aa=a/c+a/d;
	ll x=euclidean_gcd(c,d);
	x=(c*d)/x;
	aa-=a/x;
	aa=a-1-aa;
	ans-=b/x;
	ans=b-ans;
	ans-=aa;
	cout<<ans-1<<endl;
}


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