#include<bits/stdc++.h> using namespace std; string s; int main(){ cin >> s; int n = s.size(); if(s[0] >= '0' && s[0] <= '9'){ cout << "no"; return 0; } for(int i = 0; i < n; i++){ if((s[i] >= 'A' && s[i] <= 'Z') || (s[i] >= 'a' && s[i] <= 'z') || (s[i] >= '0' && s[i] <= '9') || s[i] =='_'){ // nothing }else{ cout << "no"; return 0; } } cout << "yes"; return 0; }