#include<iostream> 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; }