#include <iostream>
#include <string>
#include <vector>
#include <cmath>
using namespace std;
int main(int argc, char** argv)
{
	int n, k;
	cin >> n >> k;
	string line;
	cin >> line;
	vector<int> robot, package;
	for(int i=0; i<line.size(); i++){
		if(line[i]=='P') robot.push_back(i);
		if(line[i]=='H') package.push_back(i);
	}
	int ans=0, idxR=0, idxM=0;
	while(idxR < robot.size() && idxM < package.size()){
		if(abs(robot[idxR]-package[idxM]) <= k){
			idxR++; idxM++;
			ans++;
		}
		else if(robot[idxR] > package[idxM]) idxM++;
		else if(package[idxM] > robot[idxR]) idxR++;
	}
	cout << ans << endl;
	return 0;
}
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