#include <bits/stdc++.h>
#include <cstdlib>
#include <stdlib.h>
using namespace std;
#define ull unsigned long long
#define ld long double
#define ll long long
#define int long long
#define pii pair<int, int>
#define all(v) v.begin(), v.end()
int mod = 1e9 + 7;
const ll inf = 1e18;
const int N = 1e6 + 50, K = 22;
void solve(){
int n, k;
cin >> n >> k;
vector<ll> a(n);
for(auto & i : a)
cin >> i;
vector<ll> ans;
for(int i = 0; i < n - 1; i++)
ans.push_back(a[i + 1] - a[i] - 1);
sort(all(ans), greater<ll>());
ll res = 0;
for(int i = 0; i < k - 1; i++)
res += ans[i];
cout << a[n - 1] - a[0] + 1 - res << '\n';
}
int32_t main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int t = 1;
// cin >> t;
while(t--)
solve();
return 0;
}
