#include<bits/stdc++.h>
using namespace std;
int main()
{
int n=0;
cin>>n;
int max=1;
int mark=1;
int pre=-1;
int t=0;
for(int i=1;i<=n;i++){

cin>>t;
if(t==pre+1){mark++;}
else{if(mark>max){max=mark;}
mark=1;}
pre=t;}
cout<<max<<endl;
return 0;}