Problem:
Score : 100 points

Problem Statement

You are given a string S of length N consisting of A, B and C, and an integer K which is between 1 and N (inclusive).
Print the string S after lowercasing the K-th character in it.

Constraints

1 ≤ N ≤ 50

1 ≤ K ≤ N

S is a string of length N consisting of A, B and C.

Input

Input is given from Standard Input in the following format:

N K
S

Output

Print the string S after lowercasing the K-th character in it.

Sample Input 1

3 1
ABC

Sample Output 1

aBC

Sample Input 2

4 3
CABA

Sample Output 2

CAbA

Solution in C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <iostream>
#include <iomanip>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <algorithm>
#include <cmath>
#include <climits>
#include <math.h>
#include <bitset>

#define X first
#define Y second
#define vsort(v) sort(v.begin(), v.end())
#define vrev(v) reverse(v.begin(), v.end())
#define vmax_p(v) max_element(v.begin(), v.end())
#define vmin_p(v) min_element(v.begin(), v.end())
#define vmax_idx(v) distance(v.begin(), vmax_p(v))
#define vmin_idx(v) distance(v.begin(), vmin_p(v))
#define vcopy(src, dst) copy(src.begin(), src.end(), back_inserter(dst))
#define P pair

// stoi(s): string to int
// stod(s): string to double

// INT_MAX
// INT_MIN
// LLONG_MAX
// LLONG_MIN
// DBL_MIN
// DBL_MAX
// LDBL_MIN
// LDBL_MAX

// A-Z: 65~90
// a-z: 97~122
// |a-z| = 26

// floor(x): truncate

// 2進数変換
// string s = bitset<20>(x).to_string();

using namespace std;
using ll = long long;

int main(int argc, const char *argv[])
{
    int n, k;
    cin >> n >> k;
  
    double ans = 0;
    for (int i = 1; i <= n; i++)
    {
        int x = i;
        double y = 1;
        for (; x < k;)
        {
            x *= 2;
            y /= 2;
        }

        ans += 1.0 / n * y;
    }
    cout << setprecision(9) << ans << endl;
}