#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; getline(cin,a); char a1=a.length(); if(a[0]>='0'&&a[0]<='9'){ cout<<"no"<<endl; return 0; } int b; for(int i=0;i<a1;i++){ b=a[i]; if(!((b<='9'&&b>='0')||(b<='Z'&&b>='A')||(b<='z'&&b>='a')||(b=='_'))){ cout<<"no"<<endl; return 0; } } cout<<"yes"<<endl; return 0; }