// editor1
#include <iostream>
#include <string>

using namespace std;

bool check(string s)
{
    for(char i:s)
    {
        if(!isalnum(i) && !(i == ' ' || i == ','))
        return true;
    }
    return false;
}

int main()
{
    string s;
    getline(cin, s);
    
    if(s.size()>100)
    {
        cout << "INVALID INPUT";
        return 0
    }
    
    if(check(s))
    {
        cout << "INVALID INPUT";
        return 0;
    }
    
    string rs = "", ls = "";
    
    for(int i=s.size()-1;i>=0;i--)
    {
        if(s.at(i) == ' ' || s.at(i) == ',')
        continue;
        rs += tolower(s.at(i));
    }
    
    for(int i=0;i<s.size();i++)
    {
        if(s.at(i) == ' ' || s.at(i) == ',')
        continue;
        ls += tolower(s.at(i));
    }
    
    if(rs == ls)
    cout << "YES";
    else
    cout << "NO";
    
    return 0;
}