#include <bits/stdc++.h>
using namespace std;
const int N = 1e4 + 10;

//常数，正无穷大
const int INF = 0x3f3f3f3f;

int a[N];
int Max = -INF, len = 1;
/*
1 1

一个数字，这个数字是1
最长的连续长度是几？
1

*/
int main() {
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
        if (i > 1) {
            if (a[i] - a[i - 1] == 1)
                len++;
            else
                len = 1;
        }
        Max = max(Max, len);
    }
    cout << Max << endl;
    return 0;
}