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

    ios::sync_with_stdio(false); \
    cin.tie(nullptr), cout.tie(nullptr);
#define endl "\n"

#define ll long long

#define int long long

using i64 = int64_t;
// using i128 = __int128_t;
const int maxN = 2e5 + 10;
const int MOD = 1e9 + 7;

void solve() {
    ll a, m, l, r;
    cin >> a >> m >> l >> r;
    ll ans = 0;
    l -= a, r -= a;
    if ((l >= 0 && r >= 0) || (l <= 0 && r <= 0)) {
        if (l >= 0 && r >= 0) {
            ans += abs(r) / m - abs(l) / m;
            ans += l % m == 0;
        } else {
            ans -= abs(r) / m - abs(l) / m;
            ans += l % m == 0;
        }
    } else {
        ans += abs(r) / m + abs(l) / m + 1;
    }
    cout << ans << endl;
}

signed main() {
    FastIO int t = 1;
    // cin>>t;
    while (t--) solve();
    return 0;
}