#include <bits/stdc++.h>
using namespace std;
#define int long long
#define OYY 1000000005
#define mod 1000000007
#define faster ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define mid (start+end)/2
#define lim 200005
int32_t main(){
faster
int n,k;cin>>n>>k;
int dizi[n];
priority_queue <int> pq;
for(int i=0;i<n;i++){
cin>>dizi[i];
if(i>0)pq.push(dizi[i]-dizi[i-1]-1);
}
k--;
int cev=dizi[n-1]-dizi[0]+1;
while(k--){
cev-=pq.top();
pq.pop();
//cout<<cev<<'\n';
}
cout<<cev<<'\n';
return 0;
}
