#include <iostream>
#include <string>
#include <fstream>

using namespace std;

int main()
{
    int n,i,s1,nr,c;
    char s;
    float ma;
    s1=0;
    nr=0;
    c=0;
  ifstream f("text.in");
  ofstream g("text.out");
  while(f.get(s)){

      if(((s>='a')&&(s<='z'))||((s>='A')&&(s<='Z')))
      {
        s1=s1+1;
        c=1;
  }
      else
        if (c==1)
        {
           nr=nr+1;
            c=0;
        }
      }

  if(c==1)
    nr=nr+1;
  ma=s1/nr;
  g<<ma;
  }