#include <iostream>
#include <algorithm>

using namespace std;

const int MAXN = 1e6 + 5;
int a[MAXN];
int b[MAXN];
int sum,n,m;

int main(){
	cin >> n >> m;
	for (int i=1;i<=n;i++)
		cin >> a[i];
	
	for (int i=1;i<=n-1;i++)	b[i] = a[i+1] - a[i] - 1;
	sort(b+1,b+n);
	
	
	int ans = a[n] - a[1] + 1;
	int j = n-1;
	for (int i=1;i<=m-1;i++){
		ans -= b[j];
		j--;
	}
		
	cout << ans<< endl;
}