#include <stdio.h>
int main(){

	int n;
	scanf("%d",&n);
	int sum=1;
	int temp=-1;
	int max_sum=1;
	while(n--){
		int k;
		scanf("%d",&k);
	
		if(k-temp!=1){
			max_sum = max_sum>sum?max_sum:sum;
			sum=1;
			temp = k;
		}else {
			sum++;
			temp =k;
		}
	}
	max_sum = max_sum>sum?max_sum:sum;
	printf("%d",max_sum);


	return 0;
}