#include"fstream.h"
#include"string.h"

int main()
{
   ifstream in("text.in");
   ofstream out("text.out");
   unsigned int cuv=0, lit=0;
   char l[2];
   while(!in.eof())
   {
      in.get();
      in.get(l,2);
      if((strcmp(l,"a")>=0 && strcmp(l,"z")<=0) || (strcmp(l,"A")>=0 && strcmp(l,"Z")<=0))
	 lit++;
      else
	if(lit!=0)
	 cuv++;
   }
   out<<lit/cuv;
   in.close();
   out.close();
   return 0;
}