#include <bits/stdc++.h>
using namespace std;
#define sp " "
#define endl "\n";
#define fastio() cin.tie(0), ios_base::sync_with_stdio(0)
#define pb push_back
#define pii pair<int, int>
#define st first
#define nd second
#define N 200005
const int modulo = 1e9 + 7;
int arr[N];
int32_t main()
{
fastio();
int n, k;
cin>>n>>k;
for (int i = 1; i <= n; i++)
cin>>arr[i];
vector<int> diff;
for (int i = 2; i <= n; i++) diff.pb(arr[i] - arr[i - 1] - 1);
sort(diff.rbegin(), diff.rend());
int ans = arr[n] - arr[1] + 1;
for (int i = 0; i < k - 1; i++) ans -= diff[i];
cout<<ans<<endl;
cerr << "time taken : " << (float)clock() / CLOCKS_PER_SEC << " seconds\n";
}
