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

int main() {
    long long a, m, l, r;
    cin >> a >> m >> l >> r;
    // a + m * x1 >= l
    // a + m * x2 <= r
    /*
    m * x1 >= l - a
    x1 >= (l - a) / m
    x2 <= (r - a) / m
    */
    long long x1 = ceil(1.0 * (l - a) / m);
    long long x2 = floor(1.0 * (r - a) / m);
    cout << x2 - x1 + 1 << "\n";
    return 0;
}