#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
void DBG() { cerr << "]" << endl; }
template<class H, class... T> void DBG(H h, T... t) { cerr << to_string(h); if(sizeof...(t)) cerr << ", "; DBG(t...); }
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "]: [", DBG(__VA_ARGS__)
const int N = 1e5 + 3;
int t[N];
void solve() {
int n, k; cin >> n >> k;
vector<int> dif;
for (int i = 1; i <= n; i++) {
cin >> t[i];
if (i == 1) continue;
dif.push_back(t[i]-1-t[i-1]);
}
sort(dif.begin(), dif.end(), greater<>());
int ans = t[n]+1-t[1];
for (int i = 0; i < k-1; i++) ans -= dif[i];
cout << ans << "\n";
}
signed main() {
ios::sync_with_stdio(false); cin.tie(0);
int t=1; //cin >> t;
while (t--) {
solve();
}
}
