#include <bits/stdc++.h>
using namespace std;
template <class T>
bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  long long N, K;
  cin >> N >> K;
  vector<long long> A(N), sum(N + 1, 0);
  long long ans = 0;
  for (long long i = 0; i < N; i++) {
    cin >> A[i];
    ans += A[i];
    sum[i + 1] += sum[i] + A[i];
  }
  vector<long long> tmp;
  for (long long i = (1); i <= (N - 1); ++i) {
    tmp.push_back(sum[N] - sum[i]);
  }
  sort((tmp).rbegin(), (tmp).rend());
  for (long long i = 0; i < K - 1; i++) ans += tmp[i];
  cout << ans << endl;
  return 0;
}
