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