#include<bits/stdc++.h>
#pragma GCC optimize("unroll-loops,no-stack-protector")
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> pll;
const ll MOD=1e9+7;
const ll MOD2=998244353;
const ll N=2e4+5;
const ld pi=3.14159265359;
#define SQ(i) ((i)*(i))
#define REP(i,n) for(ll i=0;i<n;i++)
#define REP1(i,n) for(ll i=1;i<=n;i++)
#define pb push_back
#define mp make_pair
#define X first
#define Y second
#define setp setprecision
#define lwb lower_bound
#define SZ(_a) (ll)_a.size()
ll n,k,lst,x,ans;
vector<ll> v;
int main(){
ios_base::sync_with_stdio(0);cin.tie(0);
cin>>n>>k;
REP(i,n){
cin>>x;
if(i)v.pb(x-lst-1);
lst=x;
}
sort(v.begin(),v.end());
REP(i,SZ(v)-k+1)ans+=v[i];
cout<<ans+n<<"\n";
return 0;
}
