/*
Author: Nguyen Chi Thanh - High School for the Gifted - VNU.HCM (i2528)
*/
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ull unsigned long long
#define ld long double
#define pii pair<int, int>
#define fi first
#define se second
#define __builtin_popcount __builtin_popcountll
#define all(x) (x).begin(), (x).end()
#define BIT(x, i) (((x) >> (i)) & 1)
#define MASK(x) ((1ll << (x)))
#define debug(a, l, r) for (int _i = (l); _i <= (r); ++_i) cout << (a)[_i] << ' '; cout << '\n';
const int MAXN = 1e5 + 5;
int n, k, a[MAXN];
void init() {
cin >> n >> k;
for (int i = 1; i <= n; ++i) cin >> a[i];
}
void solve() {
int sum = n;
priority_queue<int, vector<int>, greater<int>> pq;
for (int i = 1; i < n; ++i) pq.push(a[i + 1] - a[i] - 1);
int joiner = n - 1;
while (joiner > k - 1) {
sum += pq.top();
pq.pop();
--joiner;
}
cout << sum;
}
signed main() {
#ifdef NCTHANH
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
ios_base::sync_with_stdio(0);
cin.tie(nullptr); cout.tie(nullptr);
init();
solve();
return 0;
}
