/*
* AUTHOR : lo0ker
* Problem :
* source :
*/
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vi = vector<int>;
using pii = pair<int, int>;
#define pb push_back
#define all(x) begin(x), end(x)
#define sz(x) (int) (x).size()
const int MOD = 1e9+7;
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int n, k;
cin >> n >> k;
vi a(n);
for(auto &it : a) cin >> it;
vi b;
for(int i = 1; i < n; i++){
b.pb(a[i] - a[i-1]);
}
sort(all(b), greater<int>());
ll ans = a[n-1] - a[0] + 1;
for(int i = 0; i < k-1; i++){
ans -= (b[i]-1);
}
cout << ans;
return 0;
}
