#ifndef Nhoksocqt1
#include "gap.h"
#endif // Nhoksocqt1
#include<bits/stdc++.h>
using namespace std;
#define inf 0x3f3f3f3f
#define sz(x) int((x).size())
#define fi first
#define se second
typedef long long ll;
typedef pair<int, int> ii;
template<class X, class Y>
inline bool maximize(X &x, const Y &y) {return (x < y ? x = y, 1 : 0);}
template<class X, class Y>
inline bool minimize(X &x, const Y &y) {return (x > y ? x = y, 1 : 0);}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int Random(int l, int r) {
return uniform_int_distribution<int>(l, r)(rng);
}
const int MAXN = 100005;
ll a[MAXN];
int nArr;
#ifdef Nhoksocqt1
ll _A[MAXN], M;
void MinMax(ll s, ll t, ll *a, ll *b) {
int l(1), r(nArr), optL(0), optR(-1);
while(l <= r) {
int mid = (l + r) >> 1;
if(_A[mid] >= s) {
optL = mid;
r = mid - 1;
} else {
l = mid + 1;
}
}
l = 1, r = nArr;
while(l <= r) {
int mid = (l + r) >> 1;
if(_A[mid] <= t) {
optR = mid;
l = mid + 1;
} else {
r = mid - 1;
}
}
assert(optL <= optR);
*a = _A[optL], *b = _A[optR];
M += optR - optL + 1;
}
#endif // Nhoksocqt1
bool check(ll dis) {
ll last(a[1]);
while(last < a[nArr]) {
ll pa, pb;
MinMax(last, last + dis - 1, &pa, &pb);
//cout << last << ' ' << last + dis - 1 << ' ' << pa << ' ' << pb << '\n';
if(pa == pb)
return true;
last = pb;
}
return false;
}
ll findGap(int T, int N) {
nArr = N;
MinMax(0, ll(1e18), &a[1], &a[nArr]);
if(T == 1) {
for (int i = 2; i <= (nArr + 1) / 2; ++i)
MinMax(a[i - 1] + 1, a[nArr - i + 2] - 1, &a[i], &a[nArr - i + 1]);
ll res(0);
for (int i = 1; i < nArr; ++i)
res = max(res, a[i + 1] - a[i]);
return res;
}
ll l(1), r(1e18), answer(0);
while(l <= r) {
ll mid = (l + r) >> 1;
if(check(mid)) {
answer = mid;
l = mid + 1;
} else {
r = mid - 1;
}
}
//cout << M << '\n';
return answer;
}
#ifdef Nhoksocqt1
int main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
freopen("GAP.inp", "r", stdin);
freopen("GAP.out", "w", stdout);
int T, N;
cin >> T >> N;
for (int i = 1; i <= N; ++i) {
cin >> _A[i];
_A[i] = _A[i - 1] + Random(1, 1e9); cout << _A[i] << " \n"[i == N];
}
M = 0;
cout << findGap(T, N);
return 0;
}
#endif // Nhoksocqt1
