#include <bits/stdc++.h>
using namespace std;
template <typename T>
using V = vector<T>;
template <typename T>
using VV = vector<V<T>>;
template <typename T>
istream &operator>>(istream &cin, V<T> &arr) {
  for (T &val : arr) {
    cin >> val;
  }
  return cin;
}
template <typename T>
ostream &operator<<(ostream &cout, VV<T> &arr) {
  for (V<T> &val : arr) {
    cout << val << endl;
  }
  return cout;
}
template <typename T>
ostream &operator<<(ostream &cout, V<T> &arr) {
  for (T &val : arr) {
    cout << val << " ";
  }
  return cout;
}
void update(vector<vector<long long>> &tree, long long v, long long l,
            long long r, long long lb, long long rb, long long val) {
  if (lb > rb) {
    return;
  }
  if (l == lb && r == rb) {
    tree[v][2] += val;
  } else {
    long long m = (l + r) / 2;
    update(tree, v * 2, l, m, lb, min(rb, m), val);
    update(tree, v * 2 + 1, m + 1, r, max(lb, m + 1), rb, val);
  }
}
void build(vector<vector<long long>> &tree, vector<long long> &arr, long long v,
           long long l, long long r) {
  if (l == r)
    tree[v] = {arr[l], arr[l]};
  else {
    long long m = (l + r) / 2;
    build(tree, arr, v * 2, l, m);
    build(tree, arr, v * 2 + 1, m + 1, r);
    tree[v][0] = max(tree[v * 2][0], tree[v * 2 + 1][0]);
    tree[v][1] = min(tree[v * 2][1], tree[v * 2 + 1][1]);
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long n, m, k;
  cin >> n >> m;
  vector<long long> arr(n);
  cin >> arr;
  vector<long long> razn(n - 1);
  for (int i = 0; i < n - 1; i++) razn[i] = arr[i + 1] - arr[i];
  sort(razn.begin(), razn.end());
  long long ans = 0;
  for (int i = 0; i < n - m; i++) ans += razn[i];
  cout << ans;
  return 0;
}
