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