#include <iostream> #include <string> #include <cctype> using namespace std; int main() { string s; cin >> s; if (isdigit(s[0])) { cout << "no" << endl; return 0; } for (char c : s) { if (!isalpha(c) && !isdigit(c) && c != '_') { cout << "no" << endl; return 0; } } cout << "yes" << endl; return 0; }