#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
struct guest
{
int start;
int end;
};
struct breakLength
{
int start;
int length;
};
int main()
{
int n; // Number of guests
int k; // Number of matches
cin >> n >> k;
vector<guest> guests(n);
vector<breakLength> breaks(n-1);
for (int i = 0; i < n; i++)
{
int temp = 0;
cin >> temp;
guests[i].start = temp;
guests[i].end = temp+1;
if (i > 0)
{
breaks[i-1].start = guests[i].start;
breaks[i-1].length = guests[i].start - guests[i-1].end; //Length of break between guests
}
}
//Order breaks by length
sort(breaks.begin(), breaks.end(), [](breakLength a, breakLength b) { return a.length > b.length; });
//Time from first guest arrives to last guest leaves
int totalTime = guests[n-1].end - guests[0].start;
//Number of breaks where stove can be turned off
int stoveOff = k - 1;
//Time stove is on
int stoveOn = totalTime;
//Remove the length of the longest breaks from the time the stove is on
for (int i = 0; i < stoveOff; i++)
{
stoveOn -= breaks[i].length;
}
cout << stoveOn << endl;
return 0;
}
