#include <iostream>
#include <vector>
#include <algorithm>
int main() {
std::ios::sync_with_stdio(false);
std::cin.tie(NULL);
int N, K;
if (!(std::cin >> N >> K)) return 0;
std::vector<long long> T(N);
for (int i = 0; i < N; ++i) std::cin >> T[i];
if (N <= 1) {
std::cout << 0 << '\n';
return 0;
}
std::vector<long long> gaps;
gaps.reserve(N - 1);
for (int i = 0; i + 1 < N; ++i) gaps.push_back(T[i+1] - T[i]);
long long total = T.back() - T.front();
if (K >= N) {
std::cout << 0 << '\n';
return 0;
}
std::sort(gaps.begin(), gaps.end(), std::greater<long long>());
long long cut = 0;
int take = std::max(0, K - 1);
for (int i = 0; i < take && i < (int)gaps.size(); ++i) cut += gaps[i];
long long ans = total - cut;
if (ans < 0) ans = 0;
std::cout << ans << '\n';
return 0;
}
