#include<iostream>
#include<cmath>
#include<algorithm>
#include<string>
#include<map>
using namespace std;
int main() {
	int n, arr[10000], sum = 1, Max = 0;
	cin >> n;
	for (int i = 0;i < n;i++) {
		cin >> arr[i];
	}
	for (int i = 1;i < n;i++) {
		if (arr[i] - arr[i - 1] == 1) {
			sum++;
		}
		else {
			sum = 1;
		}
		if (sum > Max) {
			Max = sum;
		}
	}
	cout << Max;
	return 0;
}