P2242

#include <bits/stdc++.h>
using namespace std;
int n,m,a[15001],b[15001],sum;
int main()
{
	cin >> n >> m;
    for (int i=1;i<=n;i++)
    {
        cin >> a[i];
        b[i]=a[i]-a[i-1]-1;
    }
    sum=a[n];
    sort(b+1,b+n+1);
    for (int i=n;i>=(n-m+1);i--)
    {
        sum-=b[i];
    }
    cout << sum << "\n";
	return 0;
}