#include <iostream>
using namespace std;

int long long cacu(int long long right, int long long left, int k) {
    int long long mid = left - right;
    int long long num = mid / k + 1;
    return num;
}
int main() {
    int long long a, l, r;
    int k;
    cin >> a >> k >> l >> r;
    int long long n1, n2;
    if (a < r) {
        n1 = cacu(a, r, k);
    } else {
        n1 = cacu(r, a, k);
    }
    if (a < l) {
        n2 = cacu(a, l, k);
    } else {
        n2 = cacu(l, a, k);
    }
    int long long re;
    if (a <= l) {
        re = n1 - n2;
        if ((l - a) % 3 == 0)
            re = re + 1;
    } else if (a >= r) {
        re = n2 - n1;
        if ((a - r) % 3 == 0)
            re += 1;
    } else {
        re = n1 + n2 - 1;
    }
    if (r == l) {
        if ((r - a) % 3 == 0)
            re = 1;
        else
            re = 0;
    }

    cout << re << endl;
    return 0;
}