#include<bits/stdc++.h>
#define F first
#define S second
#define MAX 500005
#define oo 1e18
#define mod 1000000007
#define fast_in ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);cout.setf(ios::fixed);cout.precision(0);
using namespace std;
typedef long long ll;
#define pll pair<ll , ll>
#define vll vector<ll>
#define vvll vector<vll>
#define vpll vector<pll>
ll n,a[MAX],k;
int main(){
fast_in
cin>>n>>k;vll v;k--;
for(int i=0;i<n;i++){
cin>>a[i];
if(i>0)v.push_back(-(a[i]-a[i-1]-1));
}sort(v.begin(),v.end());
ll r=a[n-1]+1-a[0];k=min(k,(ll)v.size());
for(int i=0;i<k;i++){
r+=v[i];
}cout<<r;
return 0;
}
