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