#include <bits/stdc++.h>
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int rnd(int l,int r){return l+rng()%(r-l+1);}
#define fasty ios_base::sync_with_stdio(0),cin.tie(0)
#define fori(x,a,b) for (int x=a;x<=b;x++)
#define ford(x,a,b) for (int x=a;x>=b;x--)
#define forv(a,b) for(auto&a:b)
#define fi first
#define se second
#define pb push_back
#define ii pair<int,int>
#define mt make_tuple
#define mp make_pair
#define all(a) a.begin(),a.end()
#define reset(f,x) memset(f, x, sizeof(f))
#define getbit(x,i) ((x>>i)&1)
#define batbit(x,i) (x|(1ll<<i))
#define tatbit(x,i) (x&~(1<<i))
#define gg exit(0);
#define int long long
const int N = 3e5+10;
int n,a[N],b[N],k;
main()
{
int n,k;
cin>>n>>k; --k;
fori(i,1,n) cin>>a[i];
fori(i,1,n-1) b[i] = a[i+1]-a[i]-1;
int res = a[n]-a[1]+1;
sort(b+1,b+n+1,greater<int>());
fori(i,1,k) res-=b[i];
cout<<res;
}
//xem lai lqdoj
//cai lai voi19
