//khodaya khodet komak kon
#include <bits/stdc++.h>
#define F first
#define S second
#define pb push_back
#define all(x) x.begin(), x.end()
#pragma GCC optimize ("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize ("-O2")
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
const int N = 200000 + 10;
const ll MOD = 1000000000 + 7;
const ll INF = 1000000010;
const ll LOG = 25;
int a[N], n, k;
int32_t main(){
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> k;
vector<int> num;
ll sm = 0;
for (int i = 1; i <= n; i++){
cin >> a[i];
if (i > 1) num.pb(a[i] - a[i - 1] - 1);
}
sm = a[n] - a[1] + 1;
sort(all(num));
reverse(all(num));
for (int i = 0; i < k - 1; i++) sm -= num[i];
cout << sm;
return 0;
}
