#include <iostream>
#include <memory.h>
#include <cstdio>
#include <time.h>

using namespace std;

const int nn = 1 << 20;
int d[nn];

long long f(long long x) {
    return x * (x+1) / 2;
}

long long memo[nn * 2];

long long h(long long n, long long m) {
    if (memo[n + m] >= 0) return memo[n + m];

    long long res = n * m;

    for (int i = 2; i <= n && i <= m; ++i)
        res += h(n / i, m / i) * -1;

    return memo[n + m] = res;
}

long long g(long long n, long long m) {
    long long res = 0;

    memset(memo, -1, sizeof memo);

    for (int a = 1; a <= n && a <= m; ++a) {
        res += h(n / a, m / a) * a;
    }

    return res;
}

long long solve(int n, int m, int a, int b) {
    long long res = f(a-1) + f(b-1) + f(n-a) + f(m-b);
    res += g(a - 1, b - 1);
    res += g(a - 1, m - b);
    res += g(n - a, b - 1);
    res += g(n - a, m - b);
    return res;
}

int main() {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);

    for (int i = 2; i < nn; ++i) if (!d[i])
        for (int j = i; j < nn; j += i) d[j] = i;

    int n, m, a, b;
    cin >> n >> m >> b >> a;
    long long res = solve(n, m, a, b);
    cout << res << endl;
    return 0;
}