// Source: https://oj.uz/problem/view/JOI18_stove
#include <bits/stdc++.h>
constexpr int mo = 100005;
long long a[mo];
int main() {
int n, k;
std::cin >> n >> k;
for (int i = 1 ; i <= n ; ++i) std::cin >> a[i];
//den noi luc t[i], roi di luc t[i] + 1?
//k que diem
//moi lan bat -> 1 que
//tong tg bat bep nho nht
//std::sort(a + 1, a + n + 1);
std::vector<long long> g;
for (int i = 1 ; i < n ; ++i) {
g.push_back(a[i + 1] - a[i] - 1);
}
std::sort(g.rbegin(), g.rend());
long long ans = a[n] - a[1] + 1;
for (int i = 0 ; i < k - 1 && i < g.size() ; ++i) {
ans -= g[i];
}
std::cout << ans;
}
/*
3 2
1
3
6
//2 que
bat diem o tg 1 -> tat o 4
bat diem o tg 6
-> tat o 7
-> total = (4 - 1) + (7 - 6) = 4:)
*/
