import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) throws FileNotFoundException {
		new Main().run();
	}
	
	long mod = (long) 1e9 + 7;

	long[] fac = new long[100];
	long[] ifac = new long[100];
	long[] inv = new long[100];
	{
		Arrays.fill(fac, 1);
		Arrays.fill(ifac, 1);
		Arrays.fill(inv, 1);
		for (int i = 2; i < 100; ++i) {
			fac[i] = i * fac[i - 1] % mod;
			inv[i] = mod - mod / i * inv[(int) (mod % i)] % mod;
			ifac[i] = inv[i] * ifac[i - 1] % mod;
		}
	}
	
	long comb(int n, int k) {
		if (k < 0 || n - k < 0) return 0;
		return fac[n] * ifac[k] % mod * ifac[n - k] % mod;
	}
	
	void run() {
		PrintWriter pw = new PrintWriter(System.out);
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int K = sc.nextInt();
		long[] A = new long[N];
		for (int i = 0; i < N; ++i) {
			A[i] = sc.nextLong();
		}
		long[] sum = new long[N + 1];
		for (int i = N - 1; i >= 0; --i) {
			sum[i] = A[i] + sum[i + 1];
		}
		long[][] B = new long[N - 1][2];
		for (int i = 0; i < N - 1; ++i) {
			B[i][0] = sum[i + 1];
			B[i][1] = i + 1;
		}
		Arrays.sort(B, (x, y) -> -Long.compare(x[0], y[0]));
		int[] rank = new int[N];
		for (int i = 0 ; i < B.length; ++i) {
			rank[(int) B[i][1]] = i;
		}
		long s = 0;
		for (int i = 0; i < K - 1; ++i) {
			s += B[i][0];
		}
		int p = K - 1;
		long ans = Long.MIN_VALUE / 3;
		for (int i = N - 1; i >= K; --i) {
			if (i != N - 1 && rank[i + 1] < p) {
				s -= sum[i + 1];
				while (B[p - 1][1] > i) ++p;
				s += B[p - 1][0];
			}
			long v = s + sum[0] - K * sum[i + 1];
			ans = Math.max(ans, v);
		}
		pw.println(ans);
		pw.close();
	}
	
	
	static void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}
}