#include <iostream>
#include <algorithm>
#include <vector>
#include <cmath>
using namespace std;
int main(){
int nInvites, nInters;
cin >> nInvites >> nInters;
vector<int> pos(nInvites), ecart(nInvites - 1);
for (int& posCur : pos)
cin >> posCur;
for (int iInvite = 0; iInvite < nInvites - 1; ++iInvite)
ecart[iInvite] = pos[iInvite + 1] - pos[iInvite];
sort(ecart.begin(), ecart.end());
int res = nInvites;
for (int iAjout = 0; iAjout < nInvites - nInters; ++iAjout)
res += ecart[iAjout] - 1;
cout << res << endl;
return 0;
}
