#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define FOR(i, l, r) for(int i = l; i <= r; i++)
#define FORD(i, l, r) for(int i = l; i >= r; i--)
#define pb push_back
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
int n, k;
cin >> n >> k;
vector<ll>a(n);
FOR(i, 0, n - 1) cin >> a[i];
if(k == n) return (cout << n << "\n"), 0;
vector<ll> ds;
FOR(i, 0, n - 2){
ll t = a[i + 1] - (a[i] + 1);
if(t > 0) ds.pb(t);
}
sort(ds.begin(), ds.end());
int ans = n;
FOR(i, 0, (int)ds.size() - (k - 1) - 1) ans += ds[i];
cout << ans << "\n";
}
