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(" "));
	
	long ans;
	long t;
	foreach(i; 0 .. n - 1){
		if(s[i] == s[i + 1]) ans += 1;
		else t += 1;
	}
	if(s[0] == 'R' || t % 2){ // 端が内向き→偶数番目をひっくり返す
		ans += min(k * 2, t);
	}
	else{ // 端が外向き→奇数番目をひっくり返す
		ans += min(k * 2, t);
	}
	
	ans.writeln;
	
}
