#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cmath>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <unordered_map>
#include <unordered_set>
#include <bitset>
#include <numeric>
#include <functional>
#include <iomanip>
#include <sstream>
#include <numeric>
#define int unsigned long long
#define pb push_back
#define be begin()
#define en end()
#define fi first
#define se second
#define makep make_pair
#define nn int n; cin>>n
#define mm int m; cin>>m
#define kk int k; cin>>k
using namespace std;
int mod=1e9+7;
void ai(vector<int> &v){
for(auto &go : v){
cin>>go;
}
}
void yesno(int k){
if(k==1){
cout<<"Yes";
}
else{
cout<<"No";
}
}
void solve(){
nn;
kk;
vector<int> arr(n);
ai(arr);
int cevap=arr[n-1]+1-arr[0];
vector<int> fark(n-1);
for(int i=0;i<n-1;i++){
fark[i]=arr[i+1]-(arr[i]+1);
}
sort(fark.be,fark.en);
reverse(fark.be,fark.en);
for(int i=0;i<k-1;i++){
cevap-=fark[i];
}
cout<<cevap<<endl;
}
signed main(){
ios::sync_with_stdio(false);
cin.tie(nullptr);
int t=1;
//cin>>t;
while(t--){
solve();
}
}
