#include<bits/stdc++.h> using namespace std; int main() { char a[25]; bool f=false,b=false; cin>>a; if(a[0]>='0'&&a[0]<='9'){ f=true; } for(int i=1;i<strlen(a);i++){ if(not((a[i]>='a'&&a[i]<='z')||(a[i]>='A'&&a[i]<='Z')||(a[i]=='_')||(a[i]>='0'&&a[i]<='9'))){ b=true; break; } } if(f||b){ cout<<"no"; }else cout<<"yes"; return 0; }