#include <bits/stdc++.h>
using namespace std;
#define int long long
#define vt vector
#define pb push_back
#define pob pop_back
#define vi vt<int>
#define vvi vt<vi>
#define vii vt<ii>
#define vvii vt<vii>
typedef long long ll;
#define For(i,a,b) for(int i = a; i < b; i++)
#define foR(i,a,b) for(int i = a; i <= b; i++)
#define roF(i,a,b) for(int i = a - 1; i >= b; i--)
#define Rof(i,a,b) for(int i = a; i >= b; i--)
priority_queue<int, vt<int>, greater<int> > pq;
signed main (){
/*
freopen(".inp","r",stdin);
freopen(".out","w",stdout);
*/
int n, k, a, b;
cin >> n >> k;
cin >> b;
For(i,1,n){
cin >> a;
pq.push(a-b-1);
b = a;
}
int sum = n;
For(i,k,n){
sum += pq.top();
pq.pop();
}
cout << sum;
}
