#include <iostream>
#include <sstream>

using namespace std;

int main()
{
    string line;
    while(getline(cin,line))
    {
       char input;
       istringstream cin(line);
	   char alpha[26]={0};
       while(cin>>input)
       {
			if(isalpha(input))
			{
				alpha[(tolower(input)-'a')]++;
			}
       }
	   int oddSum=0;
	   for(int i=0;i<26;i++)
	   {
		   oddSum += alpha[i]&1;
		   //oddSum += alpha[i]%2;
	   }

	   if(oddSum>1)
	   {
		   cout<<"no..."<<endl;
	   }
	   else
	   {
		   cout<<"yes !"<<endl;
	   }

    }

    return 0;
}