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

这把钥匙请收下！！！