#include<bits/stdc++.h>
using namespace std;

int main()
{
    int n, a;
    cin >> n;
    int pre = -1;
    int mark = 1, maxm = 0;
    for (int i = 0; i < n; i++) {
        cin >> a;
        if ((pre + 1) == a) {
            mark++;
            pre = a; // 更新 pre 的值
        } else {
            if (mark > maxm) maxm = mark;
            mark = 1;
        }
    }
    if (mark > maxm) maxm = mark;
    cout << maxm;
    return 0;
}