#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define int long long
const int MX = 2e5 + 5;
const int MOD = 1e9 + 7;
int n, k;
int a[MX];
namespace sub1{
int x[25];
vector<int> v;
int res;
void duyet(int i) {
if (i > n) {
int cnt = 0;
for (int j = 1; j <= n; j++) cnt += x[j];
if (cnt != k) return;
if (x[n] != 1) return;
v.clear();
v.push_back(a[1]);
for (int j = 1; j <= n; j++) {
if (x[j] == 1) {
v.push_back(a[j] + 1);
v.push_back(a[j + 1]);
}
}
int fn = 0;
for (int i = 0; i < v.size() - 1; i += 2) {
fn += (v[i + 1] - v[i]);
// cerr << v[i] << ' ' << v[i+1] << '\n';
}
res = min(res, fn);
// for (int j = 1; j <= n; j++) cerr << x[j] << ' ';
// cerr << '\n';
// for (auto it : v) cerr << it << ' ';
return;
}
for (int j = 0; j <= 1; j++) {
x[i] = j;
duyet(i + 1);
}
}
void solve() {
res = 1e18;
duyet(1);
cout << res;
}
}
namespace sub3{
vector<int> v;
void solve() {
for (int i = 2; i <= n; i++) {
v.push_back(a[i - 1] + 1 - a[i]);
}
sort(v.begin(), v.end());
int fn = a[n] + 1 - a[1];
for (int i = 0; i < k - 1; i++) {
fn += v[i];
}
cout << fn;
}
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
// int test; cin>>test; while (test--) {}
cin >> n >> k;
for (int i = 1; i <= n; i++) {
cin >> a[i];
}
// if (n <= 20) sub1::solve();
// else sub3::solve();
sub3::solve();
return 0;
}
// binhtinhtutinkhongcaycunhungmotkhikhongcontutinnualatuyetvong
