1 #include <cstdio>
 2 #include <iostream>
 3 #include <algorithm>
 4 #include <cstring>
 5 using namespace std;
 6 char s[1000010];
 7 int k,n,a[1000010],sum;
 8 double x,q,a1,a2,ans;
 9 int main()
10 {
11     scanf("%s %d",s,&k);
12     n=strlen(s);
13     for (int i=1;i<=n;i++)
14     {
15         a[i]=s[i-1]-‘0‘;
16         sum+=a[i];
17     }
18     x=1.0; q=(n-1.0)*n/2.0;
19     for (int i=1;i<=k;i++) x=x*(1.0-(n-1.0)/q)+(1.0-x)/q;
20     for (int i=1;i<=n;i++)
21     {
22         a1=i*(double)(n-i+1.0)/(double)(n*(n+1.0)/2.0);
23         a2=(double)a[i]*x+(double)(sum-a[i])/(double)(n-1.0)*(1.0-x);
24         ans+=a1*a2;
25     }
26     printf("%.9lf",ans);
27     return 0;
28 }