#include <bits/stdc++.h>
using namespace std;
//------------------------------DEFINE------------------------------
//******************************************************************
#define IOS ios_base::sync_with_stdio(false); cin.tie(0),cout.tie(0)
#define ll long long
#define pb push_back
#define F first
#define S second
#define INF 1e18
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define pii pair<int,int>
#define pll pair<ll,ll>
#define OK cout<<"Ok"<<endl;
#define MOD (ll)(1e9+7)
#define endl "\n"
//******************************************************************
//----------------------------FUNCTION------------------------------
//******************************************************************
ll gcd(ll a,ll b){
if(a>b) swap(a,b);
if(a==0) return a+b;
return gcd(b%a,a);
}
ll lcm(ll a,ll b){
return a/gcd(a,b)*b;
}
bool is_prime(ll n){
ll k=sqrt(n);
if(n==2) return true;
if(n<2||n%2==0||k*k==n) return false;
for(int i=3;i<=k;i+=2){
if(n%i==0){
return false;
}
}
return true;
}
//*****************************************************************
//--------------------------MAIN-CODE------------------------------
const int mxn=2e5+5;
int t=1,n,k,arr[mxn];
void solve(){
vector<int>vt;
cin>>n>>k;
for(int i=1;i<=n;i++){
cin>>arr[i];
if(i>1){
vt.pb(arr[i]-arr[i-1]-1);
}
}
sort(rall(vt));
int ans=arr[n]-arr[1]+1;
for(int i=0;i<k-1;i++){
ans-=vt[i];
}
cout<<ans<<endl;
}
int main(){
IOS;
//cin>>t;
while(t--){
solve();
}
return 0;
}
