#include <iostream> #include <string> using namespace std; int main() { bool k; string a; cin>>a; if(a[1]>='0'&&a[1]<='9'){ k=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; }