#include<iostream> #include<algorithm> using namespace std; int main() { int n; cin>>n; int a[10001]; int ans[10001]; for(int i=0;i<n;i++){ cin>>a[i]; } ans[0] = 1; for(int i=0;i<n;i++){ if(a[i]+1==a[i+1]){ ans[i+1] = ans[i]+1; } else { ans[i+1] = 1; } } sort(ans,ans+n); cout<<ans[n-1]<<endl; return 0; }