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