#include <bits/stdc++.h>
using namespace std;
#define int long long
#define INF (int)1e18
#define endl '\n'
const int mod = 1000 * 1000 * 1000 + 7;
const int N = 100005;
#define f first
#define s second
#define rep(i, a, b) for(int i = (a); i < (b); i++)
#define rrep(i, a, b) for(int i = (a); i > (b); i--)
#define vi vector<int>
#define pii pair<int, int>
//mt19937_64 RNG(chrono::steady_clock::now().time_since_epoch().count());
void Solve() {
int n , k; cin>>n>>k;
vi a(n);
for (int i = 0; i < n; ++i) {
cin>>a[i];
}
vector<int> diff;
for (int i = 0; i < n - 1; ++i) {
diff.push_back(a[i+1]-a[i]-1);
}
int ans = n;
for (int i = 0; i < n - k; ++i) {
ans += diff[i];
}
cout<< ans << endl;
}
int32_t main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
int t = 1;
// cin >> t;
for (int i = 1; i <= t; i++) {
//cout << "Case #" << i << ": ";
Solve();
}
return 0;
}
