#include<iostream>
using namespace std;
int main()
{
	int a[100],n,i,j,aux,p;
	cout<<"n="; cin>>n;
	for(i=1;i<=n;i++) cin>>a[i];
	for(i=1;i<=n;i++)
		for(j=i+1;j<=n;j++)
			if(a[i]>a[j])
			{
				aux=a[i];
				a[i]=a[j];
				a[j]=aux;
			}
	p=1;
	for(i=1;i<=n;i++) 
		if(a[i]!=i) p=0;
	if(p==1) cout<<"da";
		else cout<<"nu";
	return 0;
}