string s;
cin>>s;
int flag = 0;

bitset<26> bs(std::string("00000000000000000000000000"));

for(int i = 0 ; i < s.size(); i++)
{
    bs.flip(s[i]-'a');     
}
if((s.size() % 2 !=0) 
    && (bs.count() == 1))
{
    flag = 1; 
}
else if ((s.size() %2 == 0)
    && (bs.count() == 0))
{
    flag = 1;     
}
if(flag==0)
    cout<<"NO";
else
    cout<<"YES";
return 0;