source_code: import java.util.*;
  public class Main {
  	public static void main(String[] args) {
  		Scanner in =new Scanner(System.in);
  		int n = in.nextInt();
  		int k = in.nextInt();
  		int[] arr = new int[n];
  		for(int i = 0; i < n; i++)
  			arr[i] = in.nextInt();
  		for(int i = n-1; i > 0; i--)
  			arr[i] -= arr[i-1];
  		arr[0] = 0;
  		Arrays.sort(arr);
  		long sum = 0;
  		for(int i = n-k; i >= 0; i--)
  			sum += arr[i];
  		System.out.println(sum);
  	}
  }