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