#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int N, K;
cin >> N >> K;
vector<long long> T(N);
for (int i = 0; i < N; i++)
cin >> T[i];
vector<long long> gaps;
for (int i = 0; i + 1 < N; i++)
gaps.push_back(T[i+1] - T[i] - 1);
sort(gaps.rbegin(), gaps.rend());
long long total = T.back() + 1 - T.front();
for (int i = 0; i < K - 1 && i < (int)gaps.size(); i++)
total -= gaps[i];
cout << total << "\n";
return 0;
}
