#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
const int MAX = 2e6 + 15;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;
#define pb push_back
#define sz(x) (int) x.size()
#define fr first
#define sc second
#define mp make_pair
#define all(x) x.begin(), x.end()
#define dbg(x) cerr << #x << ": " << "[ " << x << " ]\n"
ll n, k, t[MAX];
vector<ll> dt;
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> n >> k;
for(int i = 1; i <= n; i++){
cin >> t[i];
if(i != 1) dt.pb(t[i] - t[i - 1] - 1);
}
sort(all(dt), greater<ll>());
ll ans = t[n] - t[1] + 1;
for(int i = 0; i < k - 1; i++)
ans -= dt[i];
cout << ans << '\n';
return 0;
}
