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

if __name__ == "__main__":
    main() def main():
    n,k=map(int,input().split())
    s=list(input())
    s[k-1] = s[k-1].lower()
    print("".join(s)) main 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 if __name__ == "__main__":
    main() __name__ == "__main__" __name__ "__main__" main() main def main():
    n,k=map(int,input().split())
    s=list(input())
    s[k-1] = s[k-1].lower()
    print("".join(s)) def main():
    n,k=map(int,input().split())
    s=list(input())
    s[k-1] = s[k-1].lower()
    print("".join(s)) main
def main():
    n,k=map(int,input().split())
    s=list(input())
    s[k-1] = s[k-1].lower()
    print("".join(s))

if __name__ == "__main__":
    main()