#include<bits/stdc++.h>
using namespace std;
int main()
{
ios_base::sync_with_stdio(0);
int l = 1e9,p = 0,n,k,x,po;
cin >> n >> k >> l;
po = l;
if(n == 1)
{
cout << 1 << endl;
return 0;
}
vector<int> tab;
vector<int> c;
for(int i = 1;i < n;++i)
{
cin >> x;
c.push_back(x);
}
sort(c.begin(),c.end());
for(int i = 1;i < n;++i)
{
x = c[i-1];
p = x;
tab.push_back(-(x-po-1));
po = x;
//cout << x-po-1 << endl;
}
sort(tab.begin(),tab.end());
int wyn = p-l+1;
for(int i = 1;i < k;++i)
{
wyn += tab[i-1];
}
cout << wyn;
}
