#include<iostream> short n,a[10000],ln=-1,maxn,len; int main(){ scanf("%hd",&n); for(short i=0;i<n;i++){ scanf("%hd",&a[i]); if(a[i]-1!=ln){ if(len>maxn&&len!=1) maxn=len; len=1; ln=a[i]; }else{ len++; ln=a[i]; } } printf("%hd",maxn); return 0; }