#include <bits/stdc++.h>
#if __has_include("prettyprint.hpp")
#include "prettyprint.hpp"
#endif
using namespace std;
#define ll long long
#define all(v) v.begin(), v.end()
#define watch(x) cout << (#x) << " is " << (x) << endl
#define mk make_pair
struct solve {
void main() {
ll n,k;cin>>n>>k;
vector<ll> v(n);
for (ll i=0;i<n;i++){
cin>>v[i];
}
vector<ll> a;
for (ll i=0;i<n-1;i++){
a.push_back(v[i+1]-v[i]-1);
}
sort(all(a));
reverse(all(a));
ll ans=v[n-1]-v[0]+1;
for (ll i=0;i<k-1;i++){
ans-=a[i];
}
cout<<ans<<endl;
}
};
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
ll t=1;
/* cin >> t; */
while (t--) {
solve s;
s.main();
}
return 0;
}
