#include <bits/stdc++.h>
#define int int64_t
using namespace std;
constexpr int MOD = 1e9 + 7;
void solve() {
int n, k;
cin >> n >> k;
vector <int> a(n + 1);
k--;
for(int i = 1; i <= n; i++){
cin >> a[i];
}
vector <int> v(n);
int ans = a[n] - a[1] + 1;
for(int i = 1; i < n; i++){
v[i] = a[i + 1] - a[i] - 1;
}
sort(v.begin(), v.end());
reverse(v.begin() + 1, v.end());
for(int i = 1; i <= k; i++) {
ans -= v[i];
}
cout << ans;
}
int32_t main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int tt = 1;
//cin >> tt;
while(tt--) {
solve();
}
}
