#include"stdio.h"
#include"string.h"
#include"algorithm"
using namespace std;
int n,a[10000],maxn=0,k=0;
bool buckets[1000000000];
int main(void){
    memset(buckets,0,sizeof(buckets));
    scanf("%d",&n);
    for(int i=0;i<n;i++)
        scanf("%d",&a[i]);
    sort(a,a+n);
    for(int i=0;i<n;i++)
        buckets[a[i]]=1;
    for(int i=0;i<1000000000;i++){
        if(buckets[i])
            k++;
        else{
            if(k>maxn)
                maxn=k;
            k=0;
        }
    }
    printf("%d",maxn);
    return 0;
}