#include<bits/stdc++.h>
#define int long long
using namespace std;
int a, m, l, r;
signed main(){
	//freopen("tree.in", "r", stdin);
	//freopen("tree.out", "w", stdout);
	cin >> a >> m >> l >> r;
	if(a <= l){
	   a += ((l - a - 1) / m + 1) * m;
	}else if(a > r){
		a -= ((a - r - 1) / m + 1) * m;
	}	
	int cnt = a - l;
	l += cnt % m;
	cnt = r - a;
	r -= cnt % m;
	if(r - l >= m){
		cout << (r - l) / m + 1;
	}else{
		cout << 0 << endl;
	} 
	return 0;
}