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