cycle.cpp

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#include <fstream.h>
#include <iostream.h>

ifstream fin("cycle.in");
ofstream fout("cycle.out");

const int MAX = 20+5;

int n, a[MAX];

main() {
   fin >> n;
   int i, sum1, sum2;
   for (i = 0; i < n; i++)
      fin >> a[i];
   for (sum1 = i = 0; i < n; i++, sum1++)
      if (a[i] == 0)
         break;
   for (sum2 = 0, i = n - 1; i >= 0; i--, sum2++)
      if (a[i] == 0)
         break;
   if ((sum1 & 1) || (sum2 & 1))
      fout << "YES" << endl;
   else
      fout << "NO" << endl;
   return 0;  
}