#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef long double ld;
#define pb push_back
#define pf push_front
#define fi first
#define se second
const ll mod = 1e9 + 7;
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
ll n, k;
cin >> n >> k;
k--;
vector<ll> v;
ll x;
cin >> x;
ll last = 0, fifi = x;
for (ll i = 2; i <= n; i++) {
ll xx;
cin >> xx;
v.pb(xx - x - 1);
x = last = xx;
}
sort(v.begin(), v.end());
ll ans = last - fifi + 1;
while (k--) {
ans -= max(0LL, v.back());
v.pop_back();
}
cout << ans;
}
