#include<bits/stdc++.h> using namespace std; int main(){ string a; cin>>a; int a1=a.size(),q=0; if(a[0]>='0'&&a[0]<='9'){ cout<<"no"<<endl; return 0; } for(int i=0;i<a1;i++){ if(!((a[i]<='Z'&&a[i]>='A')||(a[i]<='z'&&a[i]>='a')||(a[i]>='0'&&a[i]<='9')||(a[i]=='_'))){ cout<<"no"<<endl; return 0; } } cout<<"yes"<<endl; return 0; }