#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; }