#include <bits/stdc++.h>
using namespace std;
long long n, k, a[300005], b[300005];
int main() {
  cin >> n >> k;
  k--;
  for (int i = 1; i <= n; i++) cin >> a[i];
  for (int i = 1; i < n; i++) b[i] = a[i + 1] - a[i];
  long long res = a[n] - a[1];
  sort(b + 1, b + n);
  for (int i = n - 1; i >= n - k; i--) res -= b[i];
  cout << res;
  return 0;
}
