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