#include <iostream>
using namespace std;
int main()
{
    int n,i,count=0,max=0;
    int a[100];
    cin>>n;
    for(i=0;i<n;i++){
        cin>>a[i];
    }
    for(i=0;i<n-1;i++){
       if(a[i+1]==a[i]+1){
       	count++;
	   }else{
	   	count=0;
	   }
	   if(count>max){
	   	max=count;
	   }
    }
    cout<<max+1<<endl;
    return 0;
}