#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int n, k;
cin >> n >> k;
vector<int> arr(n);
for(int i = 0; i < n; i++){
cin >> arr[i];
}
vector<int> diff(n - 1);
for(int i = 1; i < n; i++){
diff[i - 1] = arr[i] - arr[i - 1];
}
sort(diff.begin(), diff.end());
long long answer = 0;
for(int i = 0; i < n - k ; i++){
answer += diff[i];
}
cout << answer;
return 0;
}
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