#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int N = 1e5 + 5;
ll a[N], ans;
int n, k;
vector <int> tmp;
void inp()
{
cin >> n >> k;
for (int i = 1; i <= n; i++)
cin >> a[i];
}
void solve()
{
for (int i = 2; i <= n; i++)
tmp.push_back(a[i] - a[i-1] - 1);
sort(tmp.begin(), tmp.end(), greater<int>());
for (int i = 0; i < min(k-1, (int)tmp.size()); i++)
ans += tmp[i];
cout << a[n] - a[1] + 1 - ans;
}
int main()
{
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
inp();
solve();
}
