#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
const int MAX_INVITE = 1e5;
int nbInvite, nbChange;
int tpsArrive[MAX_INVITE];
vector<int> diff;
int main()
{
ios::sync_with_stdio(false);
cin >> nbInvite >> nbChange;
for(int iInvite = 0; iInvite < nbInvite; iInvite++)
{
cin >> tpsArrive[iInvite];
if(iInvite > 0)
{
diff.push_back(tpsArrive[iInvite] - tpsArrive[iInvite - 1] - 1);
}
}
sort(diff.begin(), diff.end());
int result = tpsArrive[nbInvite - 1] - tpsArrive[0] + 1;
for(int i = nbInvite - 2; i > nbInvite - 2 - nbChange + 1; i--)
{
result -= diff[i];
}
cout << result << endl;
}
