#include <bits/stdc++.h> using namespace std; int main(){ string a; getline(cin,a); bool f = 1; if(a[0]>='0' && a[0]<='9'){ f = 0; } else{ for(int i=0;i<a.size();i++){ if(!(a[i]>='a' && a[i]<='z' || a[i]>='A' && a[i]<='Z' || a[i]>='0' && a[i]<='9'|| a[i]=='_' )){ f = 0; } } } if(f==0){ cout<<"no"; } else{ cout<<"yes"; } return 0; }