#include <bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define pb push_back
#define all(a) a.begin(), a.end()
typedef long long ll;
typedef pair<int, int> ii;
const int N = 1e5 + 5;
const int mod = 1e9 + 7;
int n, k;
ll res, a[N], b[N];
void solve()
{
cin >> n >> k;
for(int i = 1; i <= n; i++)
cin >> a[i];
for(int i = 1; i < n; i++)
b[i] = a[i + 1] - a[i] - 1;
a[n] = a[n] - a[1] + 1;
sort(b + 1, b + n, greater<ll>());
for(int i = 1; i < k; i++)
a[n] -= b[i];
cout << a[n];
}
signed main()
{
cin.tie(0)->sync_with_stdio(0);
int t = 1;
// cin >> t;
while(t--) solve();
return 0;
}
