#include <bits/stdc++.h> using namespace std; int main() { int i,t; float s,n; char a[200],b; while (scanf("%c %s",&b,a)!=EOF) { n=strlen(a); i=s=0; while (i<strlen(a)) { if (a[i]+32==b or a[i]-32==b or a[i]==b) s++; i++; } printf("%.5f\n",s/n); } return 0; }