#include<iostream>
#include<fstream>
#include<string.h>
using namespace std;

int main()
{   ifstream f("text.in");
    ofstream g("text.out");
    char s[1000001];
    float l=0,nr=0;
    bool iuytresxcvbhju =0;

    while(f.getline(s,1000000)) for(int i=0;s[i];i++){
        if(isalpha(s[i])){
            l++;
            iuytresxcvbhju=1;
        }
        else if(iuytresxcvbhju){// daca precedentul a fost litera
            iuytresxcvbhju=0;
            nr++;
        }
    }

    if(iuytresxcvbhju) nr++;

    if(nr!=0)g<<l/nr<<endl;
    else g<<0;
    f.close();
    g.close();
}