#include <bits/stdc++.h>
#define ll long long
#define pb push_back
#define all(x) x.begin(),x.end()
#define ff first
#define ss second
#define yes "Yes"
#define no "No"
#define pp pop_back
using namespace std;
void solve() {
int n,k;
cin>>n>>k;
k--;
vector<int>t(n);
for (int i=0;i<n;i++){
cin>>t[i];
}
vector<int>ivl(n);
for (int i=1;i<n;i++){
ivl[i-1]=t[i]-t[i-1]-1;
}
ivl[n-1]=1;
sort(all(ivl),greater<int>());
ll ans=2*n;
for (int i=0;i<k;i++){
ans-=ivl[i];
}
cout<<ans<<"\n";
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int t = 1;
//cin >> t;
while(t--) {
solve();
}
return 0;
}
