#include<iostream> #include<cstring> using namespace std; char a[21]; int main() { cin>>a; int b=strlen(a); bool y=1; if('0'<=a[0]&&a[0]<='9'){ y=0; } else{ for(int i=0;i<b;i++){ if(('A'<=a[i]&&a[i]<='z')||('0'<=a[i]&&a[i]<='9')||a[i]=='_'){ } else{ y=0; break; } } } if(y==1){ cout<<"yes"; } else{ cout<<"no"; } return 0; }