#include<bits/stdc++.h> using namespace std; string s; int main(){ cin >> s; if(s[0] >= '0' && s[0] <= '9'){ cout << "no"; return 0; } for(int i = 1;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] == '_')){ }else{ cout << "no"; return 0; } } cout << "yes"; return 0; }