#include <iostream>
#include <queue>
#include <bitset>
#include <stack>
#include <vector>
#include <cstring>
#include <cmath>
#include <unordered_map>
#include <map>
#include <set>
#include <algorithm>
#include <iomanip>
#define prime first
#define alpha second
#define PB push_back
#define PF push_front
#define MP make_pair
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef unsigned long long ull;
const int maxn = 1e5 + 100;
vector <int> arr;
int t[maxn];
int main (){
ios_base::sync_with_stdio (false);
int n, k;
cin >> n >> k;
for (int i = 1; i <= n; i++) {
cin >> t[i];
if (i > 1)
arr.PB (t[i] - t[i - 1] - 1);
}
sort (arr.begin(), arr.end(), greater <int> ());
ll ans = 0;
for (int i = 0; i < k - 1; i++)
ans += arr[i];
cout << t[n] - t[1] + 1 - ans << endl;
}
