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