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 (Clang 3.8.0) (judge verdict: Wrong Answer)

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

int main(){
    int N,K;
    int a;
    double b=0;
    scanf("%d %d",&N,&K);
    if(K!=2){
        for(int n=1;n<=N;n++){
            a=0;
            for(int i=1;i>0;i++){
                if(K<=n){
                    break;
                }
                if(a+1<=log2(K/n)){
                    a=a+1;
                }else{
                    a=a+1;
                    break;
                }
            }
            double p=pow(2,a);
            b=b+1/p;
        }
    }else{
        b=N-0.5;
    }
    printf("%.9lf",b/N);
    return 0;
}