#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 1e5 + 5, inf = 2e9;
int n, k, a[N], d[N];
int main() {
ios_base::sync_with_stdio(0); cin.tie(0);
// freopen(".INP", "r", stdin);
// freopen(".OUT", "w", stdout);
cin >> n >> k;
for (int i=1;i<=n;++i) cin >> a[i], d[i] = a[i] - a[i - 1] - 1;//, cout << d[i] << ' '; cout << '\n';
sort(d + 2, d + n + 1, greater<>());
// for (int i = 2; i <= n; ++i) cout << d[i] << ' '; cout << '\n';
int ans = a[n] - a[1] + 1;
for (int i = 2; i <= k; ++i) ans -= max(0, d[i]);
cout << ans;
}
