#include <bits/stdc++.h>

#define lep(i, l, r) for(int i = (l); i <= (r); i ++)
#define rep(i, l, r) for(int i = (l); i >= (r); i --)
#define debug(...) fprintf (stderr, __VA_ARGS__)

using std :: cin;
using std :: cout;
using std :: endl;
using std :: cerr;
using i64 = long long;

const int P = 998244353;
inline int mod(int x) { return x + (x >> 31 & P); }
inline void sub(int &x, int y) { x = mod(x - y); }
inline void pls(int &x, int y) { x = mod(x + y - P); }
inline int add(int x, int y) { return mod(x + y - P); }
inline int dec(int x, int y) { return mod(x - y); }
inline int power(int x, int k) {
	int res = 1; if (k < 0) k += P - 1;
	while (k) { if (k & 1) res = 1ll * res * x % P; x = 1ll * x * x % P; k >>= 1; }
	return res;
}

const int N = 1e5 + 5;

int n, a;
int b[N];

int main() {
	std :: ios :: sync_with_stdio(false);
	cin >> n >> a;
	for (int i = 1; i <= n; i ++) cin >> b[i];
	std :: vector<int> v;
	lep (i, 1, n) {
		int x = 0;
		x += (b[i] == 1);
		if (b[i == 1 ? n : i - 1] == 1) x ++;
		if (b[i == n ? 1 : i + 1] == 1) x ++;
		v.push_back (x);
	}
	std :: sort (v.begin(), v.end());
	std :: reverse(v.begin(), v.end());
	int ans = 0;
	lep (i, 0, a - 1) ans += v[i];
	ans += (n - a) * 3;
	cout << ans << endl;
	return 0;
}