//Coded by Chirath Nirodha
#include<bits/stdc++.h>
#define F first
#define S second
#define PB push_back
#define MP make_pair
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
using namespace std;
const ll mod=1e9+7;
inline void io(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
}
void solve(){
ll n,k;cin>>n>>k;
ll t[n];
vector<ll> v;
for(int i=0;i<n;i++){cin>>t[i];if(i>0)v.PB(t[i]-t[i-1]-1);}
sort(v.rbegin(),v.rend());
ll ans=t[n-1]+1-t[0];
for(int i=0;i<k-1;i++)ans-=v[i];
cout<<ans<<endl;
}
int main(){
io();
solve();
//int t;cin>>t;for(int i=0;i<t;i++)solve();
return 0;
}
