#include <iostream>
#include <cstdlib>
#include<vector>
#include<algorithm>
using namespace std;
int main()
{
string input;
vector<int> vec;
vector<int> t;
bool even;
int counter,odd;
while(cin>>input)
{
for(int i=0;i<input.length();i++)
{
if((input[i]>=97&&input[i]<=122)||(input[i]>=65&&input[i]<=90))
{
vec.push_back((int)(tolower(input[i])));
}
}
sort(vec.begin(),vec.end());
if(vec.size()%2!=0)
{
odd=0;
counter=1;
for(int i=0;i<vec.size()-1;i++)
{
if(vec[i]-vec[i+1]==0)
{
counter++;
}
else
{
t.push_back(counter);
counter=1;
}
}
if(vec[vec.size()-2]!=vec[vec.size()-1])
t.push_back(1);
for(int i=0;i<t.size();i++)
{
if(t[i]%2!=0)
odd++;
}
if(odd==1)
cout<<"yes !\n";
else
cout<<"no...\n";
}
else
{
even=true;
counter=1;
for(int i=0;i<vec.size()-1;i++)
{
if(vec[i]==vec[i+1])
{
counter++;
}
else
{
t.push_back(counter);
counter=1;
}
}
for(int i=0;i<t.size();i++)
{
if(t[i]%2!=0)
even=false;
}
if(even)
cout<<"yes !\n";
else
cout<<"no...\n";
}
vec.clear();
t.clear();
}
return 0;
}