/**
* author: hashman
* created:
**/
#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
#include "algo/debug.h"
#else
#define debug(...) 42
#endif
int32_t main() {
ios::sync_with_stdio(false);
cin.tie(0);
int n, k;
cin >> n >> k;
vector<int> t(n);
for (int i = 0; i < n; i++) {
cin >> t[i];
}
vector<int> differences;
for (int i = 0; i < n - 1; i++) {
assert(t[i] < t[i + 1]);
differences.push_back(t[i + 1] - t[i] - 1);
}
sort(differences.begin(), differences.end());
reverse(differences.begin(), differences.end());
long long ans = t[n - 1] - t[0] + 1;
for (int i = 0; i < k - 1; i++) {
ans -= 1LL * differences[i];
}
cout << ans << '\n';
}
