#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; }