#include <bits/stdc++.h>
using namespace std;
#define lalala ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define int long long int
#define N 500005
#define big 100000000000000000
#define endl "\n"
#define pb push_back
#define p push
#define f first
#define s second
signed main() {
lalala;
int n,k;cin>>n>>k;
k--;
int arr[n];
priority_queue<int>pq;
for(int i=0;i<n;i++){
cin>>arr[i];
if(i){
pq.p({arr[i]-arr[i-1]-1});
}
}
int ans=arr[n-1]-arr[0]+1;
while(k&&pq.size()){
k--;
ans-=pq.top();
pq.pop();
}
cout<<ans<<endl;
}
