//This was written by Nixat Aliyeff
#include <bits/stdc++.h>
#define ll long long
#define pb push_back
#define ff first
#define ss second
using namespace std;
void solve() {
ll n, k;
cin>>n>>k;
vector<ll>t(n);
for (ll i = 0; i < n; i++){
cin >> t[i];
}
if (n == 0) {
cout << 0 << endl;
return;
}
ll ans = (t[n - 1] + 1) - t[0];
vector<ll>diffs;
for (ll i = 0; i < n - 1; i++) {
ll gap = t[i + 1] - (t[i] + 1);
if (gap > 0) {
diffs.pb(gap);
}
}
sort(diffs.rbegin(), diffs.rend());
ll match = min((ll)diffs.size(), k - 1);
for (ll i = 0; i < match; i++) {
ans -= diffs[i];
}
cout << ans << endl;
}
int main() {
ll t=1;
while (t--) {
solve();
}
}
