#include <bits/stdc++.h>
#define int long long
#define IO ios::sync_with_stdio(0), cin.tie(0)
#define FOR(i, a, b) for (int i = a; i <= b; i++)
using namespace std;
using pii = pair<int, int>;
void dbg() {;}
template<class T, class ...U>
void dbg(T a, U ...b) { cout << a << " "; dbg(b...); }
void ent() { cout << "\n"; }
const int N = 100005;
int a[N];
signed main() {
IO;
int n, m;
cin >> n >> m;
FOR(i, 1, n) cin >> a[i];
vector<int> len;
FOR(i, 2, n)
len.push_back(a[i] - (a[i - 1] + 1));
sort(len.begin(), len.end(), greater<int>());
int ans = a[n] + 1 - a[1];
m--;
FOR(i, 0, m - 1)
ans -= len[i];
cout << ans << "\n";
return 0;
}
