#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main(){
cin.tie(NULL)->ios_base::sync_with_stdio(false);
int n, k, prev = -1, now, total;
cin >> n >> k;
vector<int> interval;
for(int i=0; i<n; i++){
if(prev == -1){
cin >> prev;
total = prev;
}else{
cin >> now;
interval.push_back(now-prev-1);
prev = now;
}
if(i == n - 1){
total = prev - total + 1;
}
}
sort(interval.begin(), interval.end(), greater<int>());
for(int i=0; i<k-1; i++){
total -= interval[i];
}
cout << total;
return 0;
}
/*
10 5
1 2 5 6 8 11 13 15 16 20
*/
