#include<iostream> using namespace std; int main(){ string s; cin>>s; int n=s.size(),sum=0; for(int i=0;i<n;i++){ if(s[0]>='0'&&s[0]<='9'){ cout<<"no"; break; }else if((s[i]>='0'&&s[i]<='9')||(s[i]>='a'&&s[i]<='z')||(s[i]>='A'&&s[i]<='Z')||s[i]=='_'){ sum++; } } if(sum==n){ cout<<"yes"; } return 0; }