rt，st表

#include <bits/stdc++.h>
#define M 100010
#define inf 0x7fffffff
using namespace std;

int n, m, l, r, k,ans;
int a[M], hmax[M][25], hmin[M][25],lg[M];

int query(int l, int r){
	int k = lg[r - l + 1];
	int Max = max(hmax[l][k], hmax[r - (1 << k) + 1][k]);
	int Min = min(hmin[l][k], hmin[r - (1 << k) + 1][k]);
	return Max - Min + l - r - 1; 
}

int main() {
    cin >> n ;
    for (int i = 1; i <= n; i++) cin >> a[i];
    for (int i = 1; i <= n; i++) hmax[i][0] = hmin[i][0] = a[i];
    for (int i=2;i<=n;i++) lg[i]=lg[i>>1]+1;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; i + (1 << j) - 1 <= n; j++) {
            hmax[i][j] = max(hmax[i][j - 1], hmax[i + (1 << (j - 1))][j - 1]);
            hmin[i][j] = min(hmin[i][j - 1], hmin[i + (1 << (j - 1))][j - 1]);
        } 
    }
    for (int i = 1; i <= n; i++)
    	for (int j = 1; j <= n; j++)
    		ans = max(ans, query(i, j));
    cout << ans; 
    return 0;
}