#include <bits/stdc++.h>
using namespace std;

using i64 = long long;

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);

#ifdef LOCAL
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif

    auto solve = [&]() {
        int n, k;
        cin >> n >> k;

        string s;
        cin >> s;

        int ans = s[0] == 'R';

        for (int i = 0; i < n - 1; i++) {
            ans += s[i] == s[i + 1];
        }

        cout << max(0, k - ans) << '\n';
    };
    
    solve();
    
    return 0;
}