#include<bits/stdc++.h>
using namespace std;
#define int long long
#define in pair<int, int>
#define f first
#define s second
#define pb push_back
#define pob pop_back
#define INF (int)1e17
#define MX (int)3e5+5
#define fast() ios_base::sync_with_stdio(false); cin.tie(NULL)
signed main()
{
fast();
int n, k;
cin >> n >> k;
vector<int> t(n+1);
for(int i = 1; i <= n; i++)
cin >> t[i];
vector<int> diff(n);
for(int i = 1; i < n; i++)
diff[i] = t[i+1]-t[i]-1;
int ans = t[n]-t[1]+1;
diff[0] = INF;
sort(diff.rbegin(), diff.rend());
for(int i = 1; i < k; i++)
ans-=diff[i];
cout << ans;
return 0;
}
