#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
#include<utility>
#include<vector>
#include<stack>
#include<queue>
#include<cstring>
#include<set>
#include<map>
#define endl "\n"
#define all(v) v.begin(),v.end()
#define st first
#define nd second
#define mp make_pair
#define pb push_back
using namespace std;
typedef long long lo;
const int mod=1000000007,N=500005;
lo a,b,c,d,e,f,g=1,h[N],arr[N];
string s;
vector<lo>v;
void solve(){
cin >> a >> b;
vector<lo>v;
for(lo i=1;i<=a;i++){
cin >> arr[i];
if(i>1)v.pb(arr[i]-arr[i-1]-1);
}
sort(all(v));
reverse(all(v));
lo ans=arr[a]-arr[1]+1;
for(lo i=0;i<b-1;i++){
ans-=v[i];
}
cout << ans << endl;
}
int main(){
#ifdef local
freopen("in.txt","r",stdin);
freopen("out.txt","w",stdout);
#endif
ios_base::sync_with_stdio(false);
cin.tie(NULL); cout.tie(NULL);
// cin >> g;
while(g--)solve();
}
