#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; cin>>a; int a1=a.length; if(a[0]<='9'&&a[0]>='0'){ cout<<"no"<<endl; return 0; } for(int i;i<a1;i++){ cher 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; }