#include <iostream> 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; }