#include<bits/stdc++.h>
using namespace std;
#define int long long
#define made return
#define in 0
#define china ;
int a[10001],n,f,s,ans;
signed main(){
	ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>s;
		a[i]=s-f;
		f=s;
	}
	for(int i=1;i<=n;i++){
		int cnt=1;
		while(a[i]==1){
			cnt++;
			i++;
		}
		ans=max(ans,cnt);
	}
	cout<<ans;
	made in china
}

#4,80分求调，用差分做的。