#include <bits/stdc++.h>
using namespace std;
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
//#pragma GCC optimize("Ofast,unroll-loops,fast-math,O3")
#define pb push_back
#define ll long long
#define int long long
//#define sz(v) int(v.size())
#define all(v) v.begin(),v.end()
int mod = 1e9 + 7;
const int N = 2e5 + 1;
const ll inf = 2e9;
void solve(){
int n,k;
cin >> n >> k;
int a[n + 1];
int sum = 1;
for(int i = 1; i <= n;i++){
cin >> a[i];
if(i != 1) sum += a[i] - a[i - 1];
}
k--;
multiset <int> mt;
int cnt = 0,ans = sum;
for(int i = 1; i < n; i++){
if(mt.size() < k){
mt.insert(a[i + 1] - a[i] - 1);
cnt += a[i + 1] - a[i] - 1;
}
else{
if(mt.size() > 0 && *mt.rbegin() < a[i + 1] - a[i] - 1){
cnt -= *mt.rbegin();
mt.erase(--mt.end());
cnt += a[i + 1] - a[i] - 1;
mt.insert(a[i + 1] - a[i] - 1);
}
}
ans = min(ans,sum - cnt);
}
cout << ans;
}
signed main(){
//freopen("time.in", "r", stdin);
//freopen("time.out", "w", stdout);
ios_base::sync_with_stdio(0);
cin.tie(0);cout.tie(0);
int t1 = 1;
while(t1--){
solve();
}
}
