import java.io.*;
import java.util.*;
public class stove{
public static void main(String[] args) throws IOException {
// br = new BufferedReader(new FileReader(".in"));
// out = new PrintWriter(new FileWriter(".out"));
//new Thread(null, new (), "peepee", 1<<28).start();
int n =readInt();
int k = readInt();
int cost = 0;
PriorityQueue<Integer> pq = new PriorityQueue<Integer>(Collections.reverseOrder());
int[] a = new int[n];
for (int i = 0; i < n; i++) a[i] = readInt();
List<Integer> st = new ArrayList<Integer>();
List<Integer> ends = new ArrayList<Integer>();
int s = a[0];
int e = a[0]+1;
st.add(s);
for (int i =1; i < n; i++) {
ends.add(e);
s = a[i];
e = a[i]+1;
st.add(s);
}
ends.add(e);
cost = ends.get(ends.size()-1) - st.get(0);
for (int i = 1; i < st.size(); i++) {
pq.add(st.get(i)-ends.get(i-1));
}
while (!pq.isEmpty() && k-->1) {
cost -= pq.poll();
}
out.println(cost);
out.close();
}
static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
static PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out));
static StringTokenizer st = new StringTokenizer("");
static String read() throws IOException{return st.hasMoreTokens() ? st.nextToken():(st = new StringTokenizer(br.readLine())).nextToken();}
static int readInt() throws IOException{return Integer.parseInt(read());}
static long readLong() throws IOException{return Long.parseLong(read());}
static double readDouble() throws IOException{return Double.parseDouble(read());}
}
