#include <bits/stdc++.h>
#define int long long
#define FOR(var,bound) for(int var = 0; var < bound; var++)
#define FORB(var,lb,ub) for (int var = lb; var < ub; var++)
#define FORR(var,bound) for(int var = bound-1; var >= 0; var--)
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef pair<int, int> pii;
int n, k;
int t[100005];
int ds[100005];
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> n >> k;
FOR (i, n) {
cin >> t[i];
}
FOR (i, n - 1) {
ds[i] = t[i+1] - t[i] - 1;
}
sort(ds, ds + n - 1);
int res = t[n - 1] - t[0] + 1;
FOR (i, k - 1) {
res -= ds[n - 2 - i];
}
cout << res << endl;
}
