#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cstring> // strcpy()\strcat()\strcmp()\strlen()\memset() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ int n,a[101],s=0,max=-1; cin>>n; for(int i=1;i<=n;i++){ cin>>a[i]; } for(int i=1;i<=n;i++){ for(int j=i+1;j<=n;j++){ if(a[i]-2==a[j]&&a[j]!=a[j+1]&&s>max){ s=j-i+1; max=s; break; } } } cout<<s; return 0; }