#include <cstring>
#include <fstream>
using namespace std;
ifstream f("text.in");
ofstream g("text.out");
int nrc,i,l,k;
double litere;
char s[10000000000];
int main()
{
    f.getline(s,10000000000);
    l=strlen(s);
    k=0;
    for (i=0;i<=l-1;i++)
    {
        if ((s[i]>='a' && s[i]<='z') || (s[i]>='A' && s[i]<='Z'))
        {
            litere++;
            k=1;
        }
        if (!((s[i]>='a' && s[i]<='z') || (s[i]>='A' && s[i]<='Z')) && k==1)
        {
            nrc++;
            k=0;
        }
        if (i==l-1 && ((s[i]>='a' && s[i]<='z') || (s[i]>='A' && s[i]<='Z')))
        {
            nrc++;
        }
    }
    g<<litere/nrc;
    f.close();
    g.close();
    return 0;
}