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