#include <iostream>
#include <algorithm>
#include <vector>
#include <math.h>
#include <cmath>
#define int long long
#define ff first
#define ss second
#define pb push_back
#define pp pop_back
#define all(x) x.begin(),x.end()
#define pii pair<int,int>
#define r0 return 0
using namespace std;
const int N = 4 * 1e5 + 5, M = 5001, MOD = 998244353, modu = 1e9 + 7;
int n,t,g,st,dr,q,l,asdw,r,d,u,k;
int nash[N],suf[N],a[N];
vector <int> v;
signed main(){
ios::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
cin >> n >> k;
for (int i = 1; i <= n; i++) {
cin >> a[i];
}
for (int i = 2; i <= n; i++) {
if (a[i] - a[i - 1] == 1) continue;
v.pb(a[i] - a[i - 1] - 1);
}
sort(all(v));
reverse(all(v));
int ans = a[n] - a[1] + 1;
for (int i = 0; i < k - 1; i++) {
ans -= v[i];
}
cout << ans << endl;
return 0;
}
//y - 1 - (x + 1) + 1
//y - 1 - x - 1 + 1
//y - x - 1;
