#include<cstdio>

#define N 30

int n,i,j,k,x,y,a[N],b[N],d[N],ans;

namespace Solve{

int flag=1,k=1,m=0,d,x,y;

int exgcd(int a,int b,int&x,int&y){

  if(!b)return x=1,y=0,a;

  int d=exgcd(b,a%b,x,y),t=x;

  return x=y,y=t-a/b*y,d;

}

void add(int a,int r){

  if(!flag)return;

  d=exgcd(k,a,x,y);

  if((r-m)%d){flag=0;return;}

  x=(x*(r-m)/d+a/d)%(a/d),y=k/d*a,m=((x*k+m)%y)%y;

  if(m<0)m+=y;

  k=y;

}

int ans(){

  if(!flag)return 0;

  return m?m:k;

}

}

int main(){

  scanf("%d",&n);

  for(i=1;i<=n;i++)a[i]=i,scanf("%d",&x),b[x]=i;

  for(y=1,i=n;i>1;i--){

    x=b[n-i+1];

    Solve::add(i,((a[x]-a[y]+1)%i+i)%i);

    for(d[x]=1,k=0,j=1;j<=n;j++)if(!d[j])a[j]=++k;

    for(y=x;d[j];)if((++y)>n)y=1;

  }

  if(ans=Solve::ans())printf("%d",ans);else puts("NIE");

  return 0;

}