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

enum MAX = 1_000_100;
ulong MOD = 1_000_000_007;
ulong INF = 1_000_000_000_000;
alias sread = () => readln.chomp();
alias Face = Tuple!(char, "dir", long, "num", bool, "edge");
alias PQueue(T, alias less = "a<b") = BinaryHeap!(Array!T, less);

void main()
{
    long n, k, i, cnt;
    scan(n, k);
    auto s = sread();
    s ~= (s[n - 1] == 'R') ? 'L' : 'R';
    auto f = new Face[](0);
    while (++i < s.length)
    {
        if (s[i - 1] == s[i])
        {
            cnt++;
        }
        else
        {
            f ~= Face(s[i - 1], cnt + 1, false);
            cnt = 0;
        }
    }
    f[0].edge = true, f[$ - 1].edge = true;
    f = f.filter!(x => x.dir != s[0]).array();
    // f.each!(x => x.writeln());
    long happy = n - 1;
    f = f[min(k, f.length) .. $];
    happy -= f.length * 2;
    // f.writeln();
    if(!f.empty && f[$ - 1].edge)
        happy++;

    happy.writeln();
}

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;
    }
}
