#include <bits/stdc++.h>
#ifndef BALBIT
#include "gap.h"
#endif // BALBIT
using namespace std;
#define ll long long
#define pii pair<int, int>
#define f first
#define s second
#define SZ(x) (int)(x.size())
#define ALL(x) (x).begin(), (x).end()
#define pb push_back
#ifdef BALBIT
#define bug(...) cerr<<"#"<<__LINE__<<" "<<#__VA_ARGS__<<": ", _do(__VA_ARGS__)
template<typename T> void _do(T && x) {cerr<<x<<endl;}
template<typename T, typename ...S> void _do(T && x, S&&...y) {cerr<<x<<", "; _do(y...);}
#define IOS()
#else
#define IOS() ios::sync_with_stdio(0), cin.tie(0)
#define endl '\n'
#define bug(...)
#endif // BALBIT
const int maxn = 1e6+5;
#ifdef BALBIT
void MinMax(ll l,ll r,ll *s, ll *t) {
bug(l,r); cin>>s>>t;
}
#endif // BALBIT
ll findGap(int T, int n) {
ll s, t;
MinMax(0, 1e18, &s, &t);
ll gp = (t-s+n-1-1) / (n-1);
bug(gp);
ll prev = s;
ll re = 0;
for (ll i = s+1; i < t; i += gp) {
ll a, b;
MinMax(i,min(i+gp-1,t),&a,&b);
if (a == -1) continue;
re = max(re, a-prev);
prev = b;
}
return re;
}
#ifdef BALBIT
signed main(){
IOS();
cout<<findGap(2,4)<<endl;
}
#endif
