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