package cn.itcast.girl.TheBlueCup_02;
import java.util.Scanner;
public class ConsecutiveNumbers {
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
int a[] = new int[n];
int sum = 1;
int max = 1;
for(int i=0;i<n;i++) {
a[i] = sc.nextInt();
}
for(int i=1;i<n;i++) {
if(a[i]==a[i-1]+1) {
sum++;
max = Math.max(max, sum);
}else {
sum = 1;
}
}
System.out.println(max);
}
}