#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, k;
  cin >> n >> k;
  vector<long long> a(n);
  for (size_t i = 0; i < n; i++) {
    cin >> a[i];
  }
  long long ans = a[n - 1] - a[0];
  multiset<long long> s;
  for (long long i = 1; i < n; i++) {
    s.insert(a[i - 1] - a[i]);
  }
  for (auto i : s) {
    if (k == 1) {
      cout << ans;
      return 0;
    } else {
      k--;
      ans += i;
    }
  }
  cout << ans;
  return 0;
}
