#include <bits/stdc++.h>
using namespace std;
#define SZ(v) ((int)(v).size())
using ll = long long;
int main(void)
{
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
int nb_personnes, nb_allumetes;
cin >> nb_personnes >> nb_allumetes;
vector<int> arrivees(nb_personnes);
for (auto &v : arrivees)
cin >> v;
ll tot_cost(arrivees.back() + 1 - arrivees[0]);
vector<int> suppresions(nb_personnes-1);
for (int i(0); i < nb_personnes-1; ++i)
suppresions[i] = arrivees[i+1] - arrivees[i]-1;
sort(suppresions.rbegin(), suppresions.rend());
for (int i(0); i < nb_allumetes-1; ++i)
tot_cost -= suppresions[i];
cout << tot_cost << endl;
}
