import std.algorithm;
import std.array;
import std.conv;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

T read(T)() { return readln.chomp.to!T; }
T[] reads(T)() { return readln.split.to!(T[]); }
alias readint = read!int;
alias readints = reads!int;

void main() {
    auto nk = readints;
    int k = nk[1];
    string s = read!string;

    auto t = s.array;
    t[k - 1] = t[k - 1].toLower();
    writeln(t);

}

