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 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main(void){
    double n, k;
    scanf("%lf %lf", &n, &k);
    long double p = 0;
    double i = n;
    double j = 0.0;
    while(i > 0){
        if(pow(2, j) * i >= k){
            p += pow(0.5, j);
            i-=1.0;
        }else{
            j+=1.0;
        }
    }
    printf("%.12Lf\n", p/n);
    return 0;
}