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