import core.bitop, std.algorithm, std.ascii, std.bigint, std.conv, std.math,
    std.functional, std.numeric, std.range, std.stdio, std.string, std.random,
    std.typecons, std.container;

T lread(T = long)()
{
    return readln.chomp.to!T();
}

T[] aryread(T = long)()
{
    return readln.split.to!(T[])();
}

void scan(TList...)(ref TList Args)
{
    auto line = readln.split();
    foreach (i, T; TList)
    {
        T val = line[i].to!(T);
        Args[i] = val;
    }
}

alias sread = () => readln.chomp();
enum MOD = 10 ^^ 9 + 7;

void main()
{
    long N,K;
    scan(N,K);
    char[] S = sread().dup;
    S[K-1] -= 'A' - 'a';
    writeln(S);
}
