#include<iostream>
#include<cctype>
using namespace std;
int main(){
    string s;
    getline(cin,s);
    if(s.length()>100){
        cout<<"INVALID INPUT";
        return 0;
    }
    if(s[0]== '-'|| s.find('.')!=string::npos){
        cout<<"INVALID INPUT:
        return 0;
    }
    string clean ="";
    for(char c:s){
        if(isalnum(c))
        clean += tolower(c);
        else if(c !=' '&& c !=','&& c !='.')
        {
            cout<<"INVALID INPUT";
            return 0;
        }
    }
    if(clean.empty()){
        cout<<"INVALID INPUT";
        return 0;
    }
    int l =0, r = clean.size() - 1;
    while(l<r){
        if (clean[l++]!= clean[r--]){
            cout<<"NO";
            return 0;
        }
    }
    cout <<"YES";
    return 0;