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