#include<bits/stdc++.h>
using namespace std;
#define endl "\n"
#define int long long
vector<int> diff;
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
int nbvisites,nballume;
cin>>nbvisites>>nballume;
nballume--;
int avant;
cin>>avant;
int rep=1;
for (int i=1;i<nbvisites;i++){
int val;
cin>>val;
diff.push_back(avant-val);
rep+=val-avant;
avant=val;
}
//cout<<rep<<endl;
sort(diff.begin(),diff.end());
for (int i=0;i<nballume;i++){
rep+=diff[i]+1;
}
cout<<rep<<endl;
return 0;
}
