#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define se second
#define fi first
#define pii pair<int,int>
#define pll pair<long long, long long>
ll k, n, fin, start, first;
vector<ll> duration;
void solve(){
cin >> n >> k;
cin >> start;
first=start;
for(int i=1; i<n; i++){
cin >> fin;
duration.push_back(fin-start);
start=fin;
}
fin-=(first-1);
sort(duration.begin(), duration.end(), greater());
k--;
for(int i=0; i<k; i++){
fin-=(duration[i]-1);
}
cout << fin << endl;
}
int main(){
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
solve();
return 0;
}
