long gcd(long a, long b)
{
  if (b == 0) return a;
  return gcd(b, a % b);
}

string solve(long n, int k, string s)
{
  int a=0,b;
  long cnt=0,sum=0;
  for (b = 0; b <= k; b++) 
    if (s[b]=='1') sum++;
  for(a=0,b=k+1;a<n;a++,b++) {
    if (s[a]=='1') cnt+=sum;
    if (a>=k) sum-=s[a-k]=='1';
    if (b<n) sum+=s[b]=='1';
  }
  long nxn = n * n, div = gcd(cnt, nxn);
  cnt /= div, nxn /= div;
  return to_string(cnt) + "/" + to_string(nxn);
}