#include <bits/stdc++.h>
using namespace std;
//~ #define int long long
#define pb push_back
#define emb emplace_back
#define fr first
#define sc second
#define all(x) x.begin(),x.end()
#define sp << " " <<
#define N 100000
#define inf (int)1e9
typedef pair<int,int> ii;
typedef tuple<int,int,int> iii;
void solve(){
int n,k;
cin >> n >> k;
int a[n];
vector<int> v;
for(int i=0;i<n;i++){
cin >> a[i];
if(i) v.pb(a[i]-a[i-1]-1);
}
int ans=a[n-1]-a[0]+1;
sort(all(v),greater<int>());
for(int i=0;i<k-1;i++)
ans-=v[i];
cout << ans << "\n";
}
int32_t main(){
//~ freopen("hopscotch.in","r",stdin);
//~ freopen("hopscotch.out","w",stdout);
cout << fixed << setprecision(0);
ios_base::sync_with_stdio(false);
cin.tie(NULL);cout.tie(NULL);
int test=1;
//~ cin >> test;
while(test--) solve();
}
