#include <bits/stdc++.h>
#define all(X) (X).begin(),(X).end()
#define rall(X) (X).rbegin(),(X).rend()
#define pub push_back
#define puf push_front
#define pob pop_back
#define pof pop_front
#define ff first
#define ss second
#define P 1000000007
#define in(x, a, b) (a <= x && x < b)
using namespace std;
using ll = long long;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<vii> vvii;
const ll inf = 1000000001, INF = (ll)1e18 + 1;
void solve() {
int n, k;
cin >> n >> k;
vi t(n);
for(int i = 0; i < n; i++) cin >> t[i];
vii dif;
for(int i = 1; i < n; i++) dif.emplace_back(t[i] - t[i - 1], i - 1);
sort(all(dif));
reverse(all(dif));
int ans = 0;
for(int i = 0; i < k - 1; i++) {
ans += t[dif[i].ss + 1] - t[dif[i].ss] - 1;
}
cout << t.back() - t[0] - ans + 1 << endl;
}
int main(){
ios_base::sync_with_stdio(false);
solve();
return 0;
}
