import sys
input = lambda : sys.stdin.readline().rstrip()

n, k = map(int, input().split())
s = list(input())
s[k - 1] = s[k - 1].lower()
print("".join(s)) import sys sys input = lambda : sys.stdin.readline().rstrip() input lambda : sys.stdin.readline().rstrip() sys.stdin.readline().rstrip() sys.stdin.readline().rstrip sys.stdin.readline() sys.stdin.readline sys.stdin sys stdin readline rstrip n, k = map(int, input().split()) n map(int, input().split()) map int input().split() ().split () input split k s = list(input()) s list(input()) list input() input s[k - 1] = s[k - 1].lower() s[k - 1] s k - 1 k 1 s[k - 1].lower() [k - 1].lower [k - 1] s k - 1 k 1 lower print("".join(s)) print "".join(s) "".join "" join s input = lambda : sys.stdin.readline().rstrip() lambda : sys.stdin.readline().rstrip() input k = map(int, input().split()) map(int, input().split()) k s = list(input()) list(input()) s n, k = map(int, input().split()) map(int, input().split()) n
import sys
input = lambda : sys.stdin.readline().rstrip()

n, k = map(int, input().split())
s = list(input())
s[k - 1] = s[k - 1].lower()
print("".join(s))