#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/detail/standard_policies.hpp>
#ifdef ONPC
#include "t_debug.cpp"
#else
#define debug(...) 42
#endif
#define allit(a) (a).begin(), (a).end()
#define sz(a) ((int) (a).size())
#define cut(s) {cout << s << '\n'; return 0;}
using namespace std;
using ll = long long;
using vi = vector<int>;
namespace pd = __gnu_pbds;
template<typename K> using ordered_set = pd::tree<K, pd::null_type, less<K>, pd::rb_tree_tag, pd::tree_order_statistics_node_update>;
template<typename... T> using hash_table = pd::gp_hash_table<T...>;
const int INF = 1e9;
const ll INFL = 1e18;
const int N = 1e5;
const int RANDOM = chrono::high_resolution_clock::now().time_since_epoch().count();
mt19937 rng(RANDOM);
int solve() {
int n, k;
cin >> n >> k;
vi t(n);
for (auto& i : t) cin >> i;
vi intervals(n-1);
for (int i = 0; i < n-1; i++) {
intervals[i] = t[i+1] - t[i] - 1;
}
sort(allit(intervals), greater<>{});
int s = 0;
for (int i = 0; i < k - 1; i++) {
s += intervals[i];
}
cout << t.back() - t.front() + 1 - s;
return 0;
}
signed main() {
cin.tie(0)->sync_with_stdio(0);
int t = 1;
//cin >> t;
while (t-- && cin) {
if (solve()) break;
#ifdef ONPC
cout << "____________________" << endl;
#endif
}
return 0;
}
