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