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