#include<iostream>
#include<string>
using namespace std;
int main(){
    string s;
    cin>>s;
    if(s[0]>='9'&&s[0]<='9'){
        cout<<"no";
        return 0;
    }
    for(int i=0;i<s.size();i++){
        if(!(s[i]>='A'&&s[i]<='Z'||s[i]>='a'&&s[i]<='z'||s[i]>='0'&&s[i]<='9'||s[i]=='_')){
            cout<<"no";
            return 0;
            
        }
    }
    cout<<"yes";
    return 0;
}