#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define st first
#define nd second
typedef long long ll;
typedef long double ld;
const ll I = 1'000'000'000'000'000'000LL;
const int II = 2'000'000'000;
const ll M = 1'000'000'007LL;
const int N = 1'000'007;
int tab[N];
void Solve()
{
int n, k, ans, x, p;
cin >> n >> k;
ans = n;
cin >> p;
for(int i = 1; i < n; ++i)
{
cin >> x;
tab[i] = x - (p + 1);
p = x;
}
sort(tab + 1, tab + n);
for(int i = 1; i <= (n - 1) - (k - 1); ++i)
ans += tab[i];
cout << ans << "\n";
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
//int t; cin >> t;
//while(t--)
Solve();
return 0;
}
