#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; if(a[0]>='0'&&a[0]<='9'){ cout<<"no"; return 0; } for(int i=0;i<a.size();i++){ if(!(a[i]>='A'&&a[i]<='Z' || a[i]>='a'&&a[i]<='z' || a[i]=='_' || a[i]>='0'&&a[i]<='9')) cout<<"no"; return 0; } } cout<<"yes"; return 0; }