#include<stdio.h>
int main()
{
    int n,a[10000],i,count=1,max=1;
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        scanf("%d",&a[i]);
    }
    for(i=2;i<=n;i++){
        if(a[i]-a[i-1]==1)
        count++;
        if(a[i]-a[i-1]!=1){
        if(count>max)
        max=count;
        count=1;}
    }
    printf("%d\n",max);
    return 0;
}