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