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: Accepted)

#include<iostream>
#include<vector>
#include<string>
#include<algorithm>
#include<list>
#include<set>
#include<map>
#include<utility>
#include<queue>

#define rep(i,x) for(ll i=0;i<(int)(x);i++)
#define reps(i,x) for(ll i=1;i<=(int)(x);i++)
#define rrep(i,x) for(ll i=((int)(x)-1);i>=0;i--)
#define rreps(i,x) for(ll i=((int)(x));i>0;i--)

#define all(x) (x).begin(),(x).end()
#define SZ(x) ((int)(x).size())
#define INF 2e9

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
typedef long long ll;
typedef std::pair<ll, ll> P;
ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}

using namespace std;

int main()
{
    ll n, k;
    string s;
    cin >> n >> k;
    cin >> s;

    string p = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    string q = "abcdefghijklmnopqrstuvwxyz";

    rep(i, p.size()){
        if(s[k-1] == p[i]){
            s[k-1] = q[i];
        }
    }

    cout << s;

    
}