#include <bits/stdc++.h>
using namespace std;
const long long BIG = 1000000000000000000LL;
void solve();
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  solve();
  return 0;
}
const long long borne = 3 * (long long)(1e5) + 5;
long long tab[borne];
long long som[borne];
long long nbElem, nbParties;
void solve() {
  cin >> nbElem >> nbParties;
  for (long long i = (0); i < (nbElem); ++i) {
    cin >> tab[i];
  }
  som[0] = tab[0];
  for (long long i = (1); i < (nbElem); ++i) som[i] = tab[i] + som[i - 1];
  vector<long long> ww(nbElem - 1);
  for (long long i = (0); i < (nbElem - 1); ++i) ww[i] = som[i];
  sort(ww.begin(), ww.end());
  long long res = nbParties * som[nbElem - 1];
  for (long long i = (0); i < (nbParties - 1); ++i) res -= ww[i];
  cout << res << "\n";
}
