#include <bits/stdc++.h>

using namespace std;

int main(){
    int n;
    while (cin >> n) {
        vector<int> a(n),dp(n,1);

        for (int i = 0; i < n; i++)cin >> a[i];
        
        int maxx = dp[0];
        for (int i = 1; i < n; i++) {
            if (a[i - 1] == (a[i] - 1)) {
                dp[i] = dp[i - 1] + 1;
            }
            maxx = max(dp[i], maxx);
        }
        cout << maxx << endl;
    }
}