/*
* With a little appreciation, in a mostly hollow tone, she says, "Delightful." As if the world has any meaning.
* TASK : Stove
* AUTHOR : Marszpace
*/
#include<bits/stdc++.h>
using namespace std;
int main(){
ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
int n,k,sum=0;
cin >> n >> k;
vector<int> deltas;
{
int prev;
cin >> prev;
sum-=prev;
for(int i=0;i<n-1;i++){
int now;
cin >> now;
deltas.push_back(now-prev-1);
prev=now;
}
sum+=prev+1;
sort(deltas.begin(),deltas.end(),greater<int>());
}
for(int i=0;i<k-1;i++){
sum-=deltas[i];
}
cout << sum;
return 0;
}
