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

#define int long long
#define vvi vector<vector<int>>
#define vec vector
#define pq priority_queue
#define all(v) (v).begin(), (v).end()
#define uniqueV(x) sort(x.begin(), x.end()); x.erase(unique(x.begin(), x.end()), x.end());
#define rep(i, n) for (int (i) = (0); (i) < (n); ++(i))
#define repp(i, m, n) for (int (i) = (m); (i) < (n); ++(i))
#define dbg(x) cerr << #x << ": " << x << endl;
#define dbg2(x, y) cerr<<"("<<#x<<", "<<#y<<") = "<<"("<<x<<", "<<y<<")"<<endl;
#define dbg3(x, y, z) cerr<<"("<<#x<<", "<<#y<<", "<<#z<<") = "<<"("<<x<<", "<<y<<", "<<z<<")"<<endl;
#define dbgB(value, size) cerr<<#value<<": "<<bitset<size>(value) << endl;
#define line() cerr << "---------------" << endl;

const int dx[] = {1, -1, 0, 0};
const int dy[] = {0, 0, -1, 1};
const double PI = 3.14159265358979323846;

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a = b; return 1; } return 0; }

template<typename T>
void print1(T begin, T end) {
	while (begin != end) {
		cerr << (*begin) << " ";
		*begin++;
	}
	cerr << endl;
}

template<typename T>
void print2(T Array, int height, int width) {
	for (int i = 0; i < height; i++) {
		for (int j = 0; j < width; j++) {
			cerr << " " << Array[i][j];
		}
		cerr << endl;
	}
}

void print() { std::cerr << endl; }
template <class Head, class... Tail>
void print(Head&& head, Tail&&... tail) {
	std::cerr << head << " ";
	print(std::forward<Tail>(tail)...);
}

template<class T>
void Add(T &a, const T &b, const T &mod=1000000007) {
	int val = ((a % mod) + (b % mod)) % mod;
	if (val < 0) { val += mod; }
	a = val;
}

template <typename X, typename T> auto vectors(X x, T a) { return vector<T>(x, a); }
template <typename X, typename Y, typename Z, typename... Zs> auto vectors(X x, Y y, Z z, Zs... zs) { auto cont = vectors(y, z, zs...); return vector<decltype(cont)>(x, cont); }

// ------------------------------------------------------------------------------------------

int a, b, c, d;

void solve() {
	int k1 = 0, k2 = 0, k3 = 0;
	int e = c * d;
	int sum = 0;
	vec<int> v, u, k;
	for (int i = a; i <= b; i++) {
		if (i % c == 0) {
			k1++;
			v.push_back(i);
		}
		if (i % d == 0) {
			k2++;
			u.push_back(i);
		}
		if (i % e == 0) {
			k.push_back(i);
			k3++;
		}
		if (i % c != 0 and i % d != 0) {
			dbg(i)
			sum++;
		}
	}
	print1(all(v));
	print1(all(u));
	print1(all(k));
	dbg(sum)
	int all = b - a + 1;
	int ans = all - k1 - k2 + k3;
	dbg(ans)
}

// long long gcd(long long a, long long b) {
//    if (b == 0) return a;
//    return gcd(b, a%b);
// }

// long long lcm(long long a, long long b) {
// 	return (a*b)/gcd(a, b);
// }

using ll = long long;
ll gcd(ll a, ll b) {
  while (a && b) {
    if (a >= b) a %= b;
    else b %= a;
  }
  return a + b;
}
//最小公倍数
ll lcm(ll a, ll b) { return (a / gcd(a, b)) * b;}

signed main() {
	cin >> a >> b >> c >> d;
	// solve();

	// Cについて
	int k1 = b/c - (a-1)/c;
	// dbg2(b/2, (a-1)/c)

	// Dについて
	int k2 = b/d - (a-1)/d;

	// Eについて
	int e = lcm(c, d);
	// dbg3(c, d, e)
	int k3 = b/e - (a-1)/e;
	// dbg2(b/e, (a-1)/e)

	// dbg3(k1, k2, k3)

	int all = b - a + 1;
	int ans = all - k1 - k2 + k3;
	cout << ans << endl;

	return 0;
}

Measured memory_bytes: 256