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