#include <bits/stdc++.h>
using namespace std;
int main()
{
int n,m;
cin >> n >> m;
m--;
int start = INT_MAX;
int stop = -1;
int cur;
cin >> cur;
start = min(start,cur);
stop = max(stop,cur);
vector<int> v;
for(int i = 1;i<n;i++){
int num;
cin >> num;
v.push_back(num-cur-1);
cur = num;
start = min(start,num);
stop = max(stop,num);
}
if(m == 0){
return (stop - start +1);
}
sort(v.begin(),v.end(),greater<int>());
// for(int i = 0;i<v.size();i++){
// cout << v[i] << " ";
// }
int ans = stop - start +1;
for(int i = 0;i<m;i++){
if(i < v.size()){
ans -= v[i];
}
}
cout << ans;
}
