#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
#include <set>
#include <map>
#define INF 1e9
using namespace std;
typedef long long ll;
void solve()
{
int n, k; cin >> n >> k;
vector<ll>v(n), a;
for (int i = 0; i < n; i++) cin >> v[i];
for (int i = 1; i < n; i++) a.push_back(v[i] - (v[i - 1] + 1));
sort(a.rbegin(), a.rend());
ll ans = (v[n - 1] - v[0]) + 1;
for (int i = 0; i < k - 1; i++) ans -= a[i];
cout << ans << "\n";
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
int t = 1;// cin>>t;
while (t--) solve();
return 0;
}
