import bisect, collections, copy, heapq, itertools, math, string, sys
input = lambda: sys.stdin.readline().rstrip() 
sys.setrecursionlimit(10**7)
INF = float('inf')
def I(): return int(input())
def F(): return float(input())
def SS(): return input()
def LI(): return [int(x) for x in input().split()]
def LI_(): return [int(x)-1 for x in input().split()]
def LF(): return [float(x) for x in input().split()]
def LSS(): return input().split()

def resolve():
    N, K = LI()
    S = list(SS())

    S[K-1] = S[K-1].lower()

    print(''.join(S))

if __name__ == '__main__':
    resolve() import bisect, collections, copy, heapq, itertools, math, string, sys bisect collections copy heapq itertools math string 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 sys.setrecursionlimit(10**7) sys.setrecursionlimit sys setrecursionlimit 10**7 10 7 INF = float('inf') INF float('inf') float 'inf' def I(): return int(input()) I def F(): return float(input()) F def SS(): return input() SS int(x) for x in input().split() for x in input().split() x input().split() ().split () input split for x in input().split() int(x) int x def LI(): return [int(x) for x in input().split()] LI int(x)-1 for x in input().split() for x in input().split() x input().split() ().split () input split for x in input().split() int(x)-1 int(x) int x 1 def LI_(): return [int(x)-1 for x in input().split()] LI_ float(x) for x in input().split() for x in input().split() x input().split() ().split () input split for x in input().split() float(x) float x def LF(): return [float(x) for x in input().split()] LF def LSS(): return input().split() LSS def resolve():
    N, K = LI()
    S = list(SS())

    S[K-1] = S[K-1].lower()

    print(''.join(S)) resolve N, K = LI() N LI() LI K S = list(SS()) S list(SS()) list SS() SS 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 if __name__ == '__main__':
    resolve() __name__ == '__main__' __name__ '__main__' resolve() resolve def LSS(): return input().split() def LSS(): return input().split() LSS def LI(): return [int(x) for x in input().split()] def LI(): return [int(x) for x in input().split()] LI def SS(): return input() def SS(): return input() SS def resolve():
    N, K = LI()
    S = list(SS())

    S[K-1] = S[K-1].lower()

    print(''.join(S)) def resolve():
    N, K = LI()
    S = list(SS())

    S[K-1] = S[K-1].lower()

    print(''.join(S)) resolve def LF(): return [float(x) for x in input().split()] def LF(): return [float(x) for x in input().split()] LF def F(): return float(input()) def F(): return float(input()) F def LI_(): return [int(x)-1 for x in input().split()] def LI_(): return [int(x)-1 for x in input().split()] LI_ INF = float('inf') float('inf') INF def I(): return int(input()) def I(): return int(input()) I input = lambda: sys.stdin.readline().rstrip() lambda: sys.stdin.readline().rstrip() input
import bisect, collections, copy, heapq, itertools, math, string, sys
input = lambda: sys.stdin.readline().rstrip() 
sys.setrecursionlimit(10**7)
INF = float('inf')
def I(): return int(input())
def F(): return float(input())
def SS(): return input()
def LI(): return [int(x) for x in input().split()]
def LI_(): return [int(x)-1 for x in input().split()]
def LF(): return [float(x) for x in input().split()]
def LSS(): return input().split()

def resolve():
    N, K = LI()
    S = list(SS())

    S[K-1] = S[K-1].lower()

    print(''.join(S))

if __name__ == '__main__':
    resolve()
