#include <bits/stdc++.h>
using namespace std;
const int N = 100005;
const long long oo = 1e18;
const int MOD = 1e9 + 7;
int n, k, t[N];
void solve(void) {
cin >> n >> k;
vector<int> vt;
for (int i = 1; i <= n; i++) {
cin >> t[i];
if (i ^ 1) vt.emplace_back(t[i] - t[i - 1] - 1);
}
sort(rbegin(vt), rend(vt));
cout << t[n] - t[1] + 1 - accumulate(begin(vt), begin(vt) + k - 1, 0);
}
signed main(void) {
ios::sync_with_stdio(false); cin.tie(nullptr);
int TEST = 1; //cin >> t;
while (TEST--) solve();
return 0;
}
