// Source : https://usxco.guide/generarl/io
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define F first
#define S second
#define PII pair<int,int>
#define pb push_back
#define sz(x) (int)(x).size()
#define tso(x) to_string(x)
#define all(x) (x).begin(), (x).end()
const int MOD = 1e9+7;
const int INF = 1e18 + 18;
const int mxN = 2e5+5;
void solve() {
int n,k; cin >> n >> k;
vector<int>ar(n);
for ( int i = 0; i<n; i++ ) cin >> ar[i];
vector<int>gap;
for (int i = 0; i<n-1; i++) gap.pb(ar[i+1]-ar[i]-1);
sort(all(gap),greater<int>());
int vl = (ar[n-1] + 1) - ar[0] , emyu = k - 1;
for ( int i = 0; i<sz(gap) && i < emyu; i++ ) vl -= gap[i];
cout << vl << endl;
}
int32_t main() {
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
solve();
return 0;
}
