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

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