/*
~2021~
*/
# include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define mp make_pair
#define fi first
#define se second
typedef long long ll;
#define pii pair<int,int>
const int N = 2e5 + 5;
const int INF = 1e9;
const ll mod = 1e9+7;
priority_queue<int>pq;
int n,k,arr[N];
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
//freopen(,r,stdin);
//freopen(,w,stdout);
cin>>n>>k;
for(int i = 1;i<=n;i++){
cin>>arr[i];
if(i > 1)pq.push(arr[i] - arr[i-1] - 1);
}
int ans = arr[n] - arr[1] + 1;
for(int i = 1;i<=k-1;i++){
ans -= pq.top();
pq.pop();
}
cout<<ans<<endl;
}
