#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>


int Max(int arr[], int n)
{
    int max = 1;

    for (int i = 0; i < n; i++) 
    {
        int tem = 1;
        if (arr[i] == arr[i - 1] + 1)
        {
            while (i < n && arr[i] == arr[i - 1] + 1) 
            {
                tem++;
                i++;
            }

            if (tem > max) 
            {
                max = tem;
            }
        }
    }

    return max;
}
int main()
{
	int n = 0;
	scanf("%d", &n);
	int* arr = (int*)malloc(n * sizeof(int));
	for (int i = 0; i < n; i++)
	{
		scanf("%d", &arr[i]);
	}
	int ret = Max(arr, n);
    printf("%d", ret);
	return 0;
}