#include <bits/stdc++.h>
#define F first
#define S second
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define int long long
using namespace std;
#ifdef LOCAL
#define WOSAOJI freopen("in.txt", "r", stdin);
#else
#define WOSAOJI ios_base::sync_with_stdio(0), cin.tie(0);
#endif
#define chmax(a, b) (a) = (a) > (b) ? (a) : (b)
#define chmin(a, b) (a) = (a) < (b) ? (a) : (b)
const int MAXN = 1e5 + 5;
int n, k;
int a[MAXN];
signed main() {
WOSAOJI
cin >> n >> k;
for (int i = 1; i <= n; i++) {
cin >> a[i];
}
priority_queue<int> pq;
for (int i = 2; i <= n; i++) {
pq.push(a[i] - a[i - 1] - 1);
}
int ans = a[n] - a[1] + 1;
k--;
while (k--) {
ans -= pq.top();
pq.pop();
}
cout << ans << '\n';
}
