#include<bits/stdc++.h> using namespace std; int main() { char s[21]; cin>>s; for(int i=0;i<strlen(s);i++){ if(s[0]>='0'&&s[0]<='9'){ cout<<'no'; return 0; } if(!(s[i]<='a'&&s[i]>='z'||s[i]<='A'&&s[i]>='Z'||s[i]=='_'||s[i]<='9'&&s[i]>='0')){ cout<<'no'; return 0; } } cout<<"yes"; return 0; }