#include<bits/stdc++.h>
#define mp make_pair
#define pb push_back
#define ii pair<int,int>
#define all(x) (x).begin(),(x).end()
#define INF 100000000000000000
#define modulo 1000000007
#define mod 998244353
#define int long long int
using namespace std;
int32_t main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
// freopen("q.gir","r",stdin);
// freopen("q.cik","w",stdout);
int n,k,ans=0;
cin>>n>>k;k--;
vector<int>arr(n);
for(int i=0;i<n;i++)cin>>arr[i];
ans=arr[n-1]-arr[0]+1;
priority_queue<int>Q;
for(int i=1;i<n;i++){
Q.push(arr[i]-arr[i-1]-1);
}
while(k--){
ans-=Q.top();
Q.pop();
}
cout<<ans;
}
