solution

#include <bits/stdc++.h>
using namespace std;
int n, k;
char c;
int ff[100005], f[100005][25][5];
int dfs(int x, int y, int z) {
    if (x == 0)
        return 0;
    if (f[x][y][z] != 0)
        return f[x][y][z];
    int s = dfs(x - 1, y, z);
    if (y != 0) {
        if (z != 0)
            s = max(s, dfs(x - 1, y - 1, 0));
        if (z != 1)
            s = max(s, dfs(x - 1, y - 1, 1));
        if (z != 2)
            s = max(s, dfs(x - 1, y - 1, 2));
    }
    if (z == ff[x])
        s++;
    f[x][y][z] = s;
    return f[x][y][z];
}
int main() {
    scanf("%d%d", &n, &k);
    for (int i = 1; i <= n; i++) {
        cin >> c;
        if (c == 'P')
            ff[i] = 0;
        else if (c == 'H')
            ff[i] = 1;
        else
            ff[i] = 2;
    }
    int s = 0;
    for (int i = 0; i <= k; i++) {
        s = max(s, max(dfs(n, i, 1), max(dfs(n, i, 2), dfs(n, i, 0))));
    }
    printf("%d", s);
}