//
//? author : Vusal Huseynov
//? created: 03.05.2025 23:46:52
//
#include "bits/stdc++.h"
// --------------------------------------------------
#define ll long long
#define all(x) x.begin(), x.end()
#define IOS \
cin.tie(0); \
cout.tie(0); \
ios_base::sync_with_stdio(0);
#define endl "\n"
// --------------------------------------------------
using namespace std;
// --------------------------------------------------
const int sz = 1e5 + 5;
const int MOD = 1e9 + 7;
void solve()
{
int n, k;
cin >> n >> k;
vector<int> a(n);
for (int &x : a)
cin >> x;
vector<int> b;
for (int i = 1; i < n; i++)
{
b.push_back(a[i] - a[i - 1] - 1);
}
sort(all(b), greater<int>());
//! Debug
// for (int i = 0; i < n - 1; i++)
// {
// cout << b[i] << " ";
// }
int sum = 0;
for (int i = 0; i < k - 1; i++)
{
sum += b[i];
}
int res = a.back() - a.front() - sum + 1;
cout << res << endl;
}
signed main()
{
IOS;
solve();
return 0;
}
