#include <bits/stdc++.h>
using namespace std;
const long long inf = 1e9 + 7;
const long long INF = 1LL << 60;
const long long mod = 1e9 + 7;
const long double eps = 1e-8;
const long double pi = acos(-1.0);
template <class T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
void solve() {
  long long n, k;
  cin >> n >> k;
  vector<long long> a(n), sum(n - 1, 0);
  long long now = 0;
  for (long long i = 0; i < n; i++) {
    cin >> a[i];
    if (i + 1 < n) now = now + a[i];
    sum[i] = now;
  }
  long long ans = k * (sum[n - 1] + a[n - 1]);
  sort(sum.begin(), sum.end());
  for (long long i = 0; i < k - 1; i++) {
    ans -= sum[i];
  }
  cout << ans << endl;
}
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  solve();
  return 0;
}
