#include<iostream>
#include<string>
#include<cctype>
using namespace std;

int main()
{
    string s;
    getline(cin, s);
    
    string clean = "";
    
    for(char c : s)
    {
        if(isalnum(c))
        clean += tolower(c);
        else if(!(c==' ' || c==','))
        {
            cout<< "INVALID INPUT";
            return 0;
        }
    }
    if(clean == "")
    {
        cout << "INVALID INPUT";
        return 0;
    }
     string rev = clean;
     reverse(rev.begin(), rev.end());
     
     if(clean == rev)
     cout << "YES";
     else
     cout << "NO";
     return 0;
}