RT，给组 hack 数据也行啊

// Problem: B - Christmas Trees
// Contest: AtCoder - UNIQUE VISION Programming Contest 2023 Christmas (AtCoder Beginner Contest 334)
// URL: https://atcoder.jp/contests/abc334/tasks/abc334_b
// Memory Limit: 1024 MB
// Time Limit: 2000 ms

#include<bits/stdc++.h>
using namespace std;
long long a,m,l,r;
long long cnt;
int main(){
	cin>>a>>m>>l>>r;
	a+=1000000000000000000;l+=1000000000000000000;r+=1000000000000000000;
	long long dis=r-l;
	long long py=min(abs(r-a)%m,abs(l-a)%m);
	dis-=py;
	if(dis<0)
		cout<<0<<endl;
	else
		cout<<dis/m+1;
	return 0;
}