#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int MAXN = 100005;
ll T[MAXN];
ll gaps[MAXN];
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int N, K;
cin >> N >> K;
for (int i = 1; i <= N; i++) {
cin >> T[i];
}
ll total_time = (T[N] + 1) - T[1];
int gap_count = 0;
for (int i = 1; i < N; i++) {
ll gap = T[i + 1] - (T[i] + 1);
if (gap > 0) {
gaps[++gap_count] = gap;
}
}
sort(gaps + 1, gaps + gap_count + 1, greater<ll>());
ll saved = 0;
for (int i = 1; i <= min(K - 1, gap_count); i++) {
saved += gaps[i];
}
ll answer = total_time - saved;
cout << answer << "\n";
return 0;
}
