#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
const int N=100010;
int q[N];
int n,si;
//判断小根堆（迭代写法)
bool judge_heap(int arr[],int n)
{
    for(int i=1;i<=n/2;i++)
    {
        if(2*i+1<=n&&q[2*i+1]<q[i])return false;
        if(2*i<=n&&q[2*i]<q[i])return false;
    }
    return true;

}
//判断小根堆(递归写法，类似于先序遍历)
bool judge_heap(int arr[],int n,int u)
{
    if(u>n)return true;
    int left=u*2;
    int right=u*2+1;
    bool is_heap=true;
    if(left<=n)
    {
        if(q[left]<q[u])return false;
        is_heap=judge_heap(arr,n,u*2);
        if(!is_heap)return false;
    }
    if(right<=n)
    {
        if(q[right]<q[u])return false;
        is_heap=judge_heap(arr,n,u*2+1);
        if(!is_heap)return false;
    }
    // 当前节点及其子树都满足小根堆
    return true;
}
int main() {
    cin>>n;
    for(int i=1;i<=n;i++)cin>>q[i];
        if(judge_heap(q,n,1))
    {
        cout<<"是小根堆"<<endl;
    }
    else
    {
        cout<<"不是小根堆"<<endl;
    }
    // if(judge_heap(q,n))
    // {
    //     cout<<"是小根堆"<<endl;
    // }
    // else
    // {
    //     cout<<"不是小根堆"<<endl;
    // }

}