#include <bits/stdc++.h>
#define int long long
//#define cout cout << "Test: "
int sum=0;
using namespace std;
void solve(){
int n,k;cin>>n>>k;
vector<int> v(n);
vector<int> ara(n-1);
for(int i=0;i<n;i++){
cin>>v[i];
if(i==0){
continue;
}
ara[i-1]=v[i]-v[i-1]-1;
}
if(n==k){
cout<<n;
return;
}
if(k==1){
cout<<v[n-1];
return;
}
sort(ara.begin(),ara.end());
for(int i=n-2;i>=n-k;i--){
//cout<<"aaaaaa";
sum+=ara[i];
}
cout<<v[n-1]-sum;
}
signed main(){
//ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
int t=1;
//cin>>t;
while(t--){
solve();
}
return 0;
}
