#include <bits/stdc++.h>
using namespace std ;
#define is ==
#define isnt !=
#define endl '\n'
#define ll long long
//4557430888798830399
void Solve () {
ll n, k ;
cin >> n >> k ;
k -- ;
ll x [n] ;
for (int i = 0 ; i < n ; i ++) cin >> x [i] ;
priority_queue <ll> pq ;
for (int i = 1 ; i < n ; i ++) pq.push (x [i] - x [i - 1] - 1) ;
ll ans = x [n - 1] - x [0] + 1 ;
while (k) {
ans -= pq.top () ;
pq.pop () ;
k -- ;
}
cout << ans << endl ;
}
int main () {
ios_base::sync_with_stdio (false) ; cin.tie (nullptr) ; cout.tie (nullptr) ;
Solve () ;
}
