#include<cstdio>
main(){int n,r,m=1,c=1,a[2020];scanf("%d",&n);for(int i=0;i<n;++i){scanf("%d",&a[i]);}r=a[1]-a[0];for(int i=0;i+1<n;++i){if(r==a[i+1]-a[i]){c++;}else{m=m<c?c:m;c=2;r=a[i+1]-a[i];}}m=m<c?c:m;printf("%d\n",m);}