#include <bits/stdc++.h>
#define ll long long
using namespace std;
const ll LEN = 1005;
vector<ll> times;
int main() {
ll n, k;
cin >> n >> k;
ll a;
for (int i = 0; i < n; i++) {
cin >> a;
times.push_back(a);
}
priority_queue<ll, vector<ll>, greater<ll>> pq;
for (int i = 1; i < k; i++) pq.push(0);
ll cnt = (ll)1e18 - 1;
for (int i = times.size() - 1; i > 0; i--) {
pq.push(times[i] - times[i-1] - 1);
pq.pop();
cnt -= times[i] - times[i-1];
}
ll sol = (ll)1e18 - cnt;
while (pq.size()) {
sol -= pq.top(); pq.pop();
}
cout << sol << endl;
return 0;
}
