#include <bits/stdc++.h>
#include <cstdio>
#define int long long
using namespace std;
void solve() {
int n;
cin >> n;
int k;
cin >> k;
vector <int> val(n);
for (int i = 0; i < n; ++i) {
cin >> val[i];
}
vector <int> d;
for (int i = 1; i < n; ++i) {
d.push_back(val[i] - val[i - 1] - 1);
}
sort(d.begin(), d.end());
for (int i = 0; i < k - 1; ++i) {
d.pop_back();
}
int ans = 0;
for (int i = 0; i < d.size(); ++i) {
ans += d[i];
}
cout << ans + n << '\n';
}
signed main() {
cin.tie(0);
ios::sync_with_stdio(false);
int t = 1;
// cin >> t;
for (int i = 0; i < t; ++i) {
solve();
}
}
