// Success consists of going from failure to failure without loss of enthusiasm
#include <bits/stdc++.h>
using namespace std;
#define nl '\n'
int main() {
cin.tie(0)->sync_with_stdio(0);
int N, K; cin >> N >> K;
vector<int> gaps;
int t; cin >> t;
int ans = -t;
for(int i = 1; i < N; i++) {
int x; cin >> x;
gaps.push_back(x-t-1);
t = x;
}
// for(auto x : gaps) cout << x << " ";
sort(rbegin(gaps), rend(gaps));
ans += t+1;
for(int i = 0; i < min(K-1, int(size(gaps))); i++) ans -= gaps[i];
cout << ans << nl;
return 0;
}
