/*
author : TIT_manh
*/
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <queue>
#include <stack>
#include <deque>
#include <bitset>
#include <numeric>
#include <functional>
#include <cassert>
#include <sstream>
#include <climits>
#define ll long long
#define FOR(i,l,r) for (int i = l; i <= r; i++)
#define FOD(i,r,l) for (int i = r; i >= l; i--)
#define fi first
#define se second
#define pb push_back
#define endl "\n"
using namespace std;
const int maxn = 1e5 + 5;
int n, k, a[maxn];
priority_queue<int> pq;
void I_love() {
cin >> n >> k;
FOR(i,1,n) {
cin >> a[i];
if (i != 1) pq.push(a[i] - a[i - 1] - 1);
}
}
void tvka() {
ll res = a[n] - a[1] + 1, tmp = 1;
while (tmp < k) {
tmp++;
res -= pq.top();
pq.pop();
}
cout << res;
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
I_love(); tvka();
return 0;
}
/*
████████╗ ██╗ ██╗ ██╗ ██╗ █████╗
╚══██╔══╝ ██║ ██║ ██║ ██╔╝ ██╔══██╗
██║ ██║ ██║ █████╔╝ ███████║
██║ ██║ ██║ ██╔═██╗ ██╔══██║
██║ ╚██╔╝ ██║ ██╗ ██║ ██║
╚═╝ ╚══╝ ╚═╝ ╚═╝ ╚═╝ ╚═╝
*/
