//designed by tooxpert
#include<bits/stdc++.h>
#define ll long long
#define vl vector<ll>
#define sl set<ll>
#define all(v) v.begin(), v.end()
#define pb push_back
#define s second
#define f first
#define pll pair<ll, ll>
#define pii pair<int, int>
using namespace std;
int main()
{
ll n, k, i, s;
cin >> n >> k;
vl v(n);
for(ll&h : v) cin >>h;
priority_queue<int>pq;
for(i = 1; i < n; i++) pq.push(v[i]-v[i-1]-1);
s = v[n-1] - v[0] + 1;
for(i = 0; i < k - 1; i++)
{
auto p = pq.top();
pq.pop();
s -= p;
}
cout << s <<endl;
}
