#include <bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update>ordered_set;
#define int long long
#define sz(x) (int)(x.size())
#define debug(x) cerr << (#x) << ": " << (x) << endl
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
int n, k, m;
vector<int> a;
string s;
void solve() {
cin >> n >> k;
a.clear();
a.resize(n);
for (auto &u: a) cin >> u;
priority_queue<int> pq;
for (int i=0; i<n-1; i++) pq.push(abs(a[i]-a[i+1])-1);
int ans=a.back()-a[0]+1;
while (--k && !pq.empty()) {
ans-=pq.top(), pq.pop();
}
cout << ans << endl;
return;
}
signed main() {
ios::sync_with_stdio(0);
cin.tie(0);
int tt=1;// cin >> tt;
while(tt--) solve();
return 0;
}
