#include <bits/stdc++.h>
#define ll long long
using namespace std;
ll a,m,l,r,ml,mr;
int main(){
	cin >> a >> m >> l >> r;
	a%=m;
	ml=l%m;
	mr=r%m;
	l+=(m+a-ml)%m;
	r-=(m+mr-a)%m;
	ll t=0;
	cout << max(t,(r-l)/m+1);
	return 0;
}