#include <bits/stdc++.h>
using namespace std;
#define int long long
void solve(){
int n, k;
cin >> n >> k;
vector<int> a(n);
for(int i = 0; i < n; i++) cin >> a[i];
vector<int> diff;
for(int i = 1; i < n; i++){
diff.push_back(a[i]-a[i-1]-1);
}
sort(diff.rbegin(), diff.rend());
int total = a[n-1] - a[0] + 1;
for(int i = 0; i < k-1; i++){
total -= diff[i];
}
cout << total << endl;
}
int32_t main(){
ios_base::sync_with_stdio(false); cin.tie(nullptr);
int t = 1;
// cin >> t;
while(t--) solve();
return 0;
}
