#include "bits/stdc++.h"
using namespace std;
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n, k;
cin >> n >> k;
vector<int> v(n);
for (auto &e:v) cin >> e;
vector<pair<int,int>> intervals;
int l = v[0], r = v[0] + 1;
int cur = v[0];
for (int i=1; i<n; i++) {
if (v[i] == cur+1) {
r = v[i] + 1;
}
else {
intervals.push_back({l,r});
l = v[i];
r = v[i] + 1;
}
cur = v[i];
}
intervals.push_back({l,r});
int sz = intervals.size();
int sum = 0;
for (auto &e:intervals) {
sum += (e.second - e.first);
}
vector<int> gap;
for (int i=1; i<sz; i++) {
int dif = intervals[i].first - intervals[i - 1].second;
gap.push_back(dif);
sum += dif;
}
sort(gap.rbegin(),gap.rend());
for (int i=0; i<min(k-1,(int)gap.size()); i++) {
sum -= gap[i];
}
cout << sum;
}
