#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cstring> // strcpy()\strcat()\strcmp()\strlen()\memset() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main() { string a; char b; getline(cin, a); int a1 = a.length(); if (a[0] <= '9' && a[0] >= '0') { cout << "No" << endl; return 0; } for (int c = 0; c < a1; c++) { b = a[c]; if (!((b <= '9' && b >= '0') || (b <= 'z' && b >= 'a') || (b <= 'Z' && b >= 'A') || (b == '_'))) { cout << "No" << endl; return 0; } } cout << "Yes" << endl; return 0; }