#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int n;
ll t,e,ans,cnt = 1;
int main(){
    cin >> n >> t;
    for(int i = 1;i < n;i++) {
        cin >> e;
        if(e - t != 1) {
            ans = max(ans,cnt);
            cnt = 1;
        }else cnt++;

        t = e;
    }

    cout << ans << endl;
    return 0;
}