progr

#include <iostream>

using namespace std;

int main()
{
int a,b,c,rat,ok=1;
cin>>a>>b;
rat=b-a;
do {

if (b-a!=rat)
  ok=0;
a=b;
cin>>b;
} while (b!=0);
if (ok)
cout<<"da";
else
    cout<<"nu";

return 0;
}