#include <bits/stdc++.h>
//#define HOME
#ifndef HOME
#include "gap.h"
#else
long long findGap(int, int);
namespace grader {
static void my_assert(int k){ if (!k) exit(1); }
static int subtask_num, N;
static long long A[100001];
static long long call_count;
void MinMax(long long s, long long t, long long *mn, long long *mx)
{
int lo = 1, hi = N, left = N+1, right = 0;
my_assert(s <= t && mn != NULL && mx != NULL);
while (lo <= hi){
int mid = (lo+hi)>>1;
if (A[mid] >= s) hi = mid - 1, left = mid;
else lo = mid + 1;
}
lo = 1, hi = N;
while (lo <= hi){
int mid = (lo+hi)>>1;
if (A[mid] <= t) lo = mid + 1, right = mid;
else hi = mid - 1;
}
if (left > right) *mn = *mx = -1;
else{
*mn = A[left];
*mx = A[right];
}
if (subtask_num == 1) call_count++;
else if (subtask_num == 2) call_count += right-left+2;
}
void grader() {
FILE *in = stdin, *out = stdout;
my_assert(2 == fscanf(in, "%d%d", &subtask_num, &N));
my_assert(1 <= subtask_num && subtask_num <= 2);
my_assert(2 <= N && N <= 100000);
for (int i=1;i<=N;i++) my_assert(1 == fscanf(in, "%lld", A+i));
for (int i=1;i<N;i++) my_assert(A[i] < A[i+1]);
fprintf(out, "Gap : %lld\n", findGap(subtask_num, N));
fprintf(out, "Calls: %lld\n", call_count);
}
}
void MinMax(long long s, long long t, long long *mn, long long *mx) {
grader::MinMax(s, t, mn, mx);
}
int main()
{
grader::grader();
}
#endif
const int MAX_N = 100000;
const long long INF = 1000000000000000000LL;
long long v[MAX_N];
long long findGap(int T, int N) {
int top = 0;
long long mn, mx, mnAll;
if(T == 1) {
MinMax(0, INF, &mn, &mx);
v[0] = mn;
v[N - 1] = mx;
for(int i = 1; i <= (N - 1) / 2; ++i) {
MinMax(v[i - 1] + 1, v[N - i] - 1, &mn, &mx);
v[i] = mn;
v[N - i - 1] = mx;
}
top = N;
} else {
MinMax(0, INF, &mn, &mx);
//printf("%lld %lld\n", mn, mx);
mnAll = mn;
long long expect = (mx - mn) / (N - 1) + 1;
for(int i = 0; i < N - 1; ++i) {
MinMax(mnAll + i * expect, mnAll + i * expect + expect - 1, &mn, &mx);
//printf("%lld %lld %lld %lld\n", mnAll + i * expect, mnAll + i * expect + expect - 1, mn, mx);
if(mn != -1)
v[top++] = mn;
if(mn != mx && mx != -1)
v[top++] = mx;
}
}
//for(int i = 0; i < top; ++i)
// printf("%lld ", v[i]);
long long rez = 0LL;
for(int i = 0; i < top - 1; ++i)
rez = std::max(rez, v[i + 1] - v[i]);
return rez;
}
