#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=0; i<s.size(); i++) { if(s[i]!='_'&&s[i]<'0'&&s[i]>'9'&&s[i]<'A'&&s[i]>'Z'&&s[i]<'a'&&s[i]>'z') { cout<<"no"; return 0; } } cout<<"yes"; return 0; }