import std.stdio, std.conv, std.string, std.array, std.range, std.algorithm, std.container;
import std.math, std.random, std.bigint, std.datetime, std.format;
void main(string[] args){ if(args.length > 1) if(args[1] == "-debug") DEBUG = 1; solve(); }
void log()(){ writeln(""); } void log(T, A ...)(T t, lazy A a){ if(DEBUG) write(t, " "), log(a); } bool DEBUG = 0;
string read(){ static string[] ss; while(!ss.length) ss = readln.chomp.split; string res = ss[0]; ss.popFront; return res; }
T rtype(T)(){ return read.to!T; } alias rint = rtype!int, rlong = rtype!long, rreal = rtype!real;
T[] rtypes(T)(int n){ return n.iota.map!(i => rtype!T()).array; } alias rint = rtypes!int, rlong = rtypes!long, rreal = rtype!real;
// ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- //
void solve(){
	int n = rint, k = rint;
	string s = read;
	bool[] xs = s.map!(c => c == 'R').array;
	log("xs:", xs.map!(x => x? "R": "L").array.join(" "));
	
	int RR, LL, LR, RL, ZL, ZR, LZ, RZ;
	foreach(i; 0 .. n - 1){
		if(xs[i] && xs[i + 1]) RR += 1;
		else if(! xs[i] && ! xs[i + 1]) LL += 1;
		else if(xs[i] && ! xs[i + 1]) RL += 1;
		else if(!xs[i] && xs[i + 1]) LR += 1;
	}
	if(! xs[0]) ZL = 1;
	if(xs[0]) ZR = 1;
	if(! xs[n - 1]) LZ = 1;
	if(xs[n - 1]) RZ = 1;
	log("RR:", RR, "LL:", LL, "RL:", RL, "LR:", LR);
	
	int ans = LL + RR + min(RL * 2 + max(RZ, ZL), LR * 2 + max(LZ, ZR) , k * 2);
	
	ans.writeln;
	
}
