#include <bits/stdc++.h>
#include <algorithm>
#include <iostream>
#include <string>
using namespace std;
#define FOR(i,n) for(int i=0;i<n;i++)
#define ROF(i,m,n) for(int i=m;i<=n;i++)
#define vi vector<int>
#define pb push_back
#define alle(a) a.begin(),a.end()
#define all(n) begin(n), end(n)
#define rall(n) rbegin(n),rend(n)
#define int long long
#define vecs vector<int>
#define ll long long
#define ss second
#define ff first
const int INF = 1e18;
const int MOD = 1e9 + 7;
void solve(){
int n, k;
cin>>n>>k;
vector <int> t(n);
for(int i = 0;i < n;i++){
cin>>t[i];
}
vector <int> of;
for(int i = 0;i < n - 1;i++){
of.pb(t[i + 1] - t[i] - 1);
}
sort(of.rbegin(),of.rend());
k--;
int ans = t[n - 1] + 1 - t[0];
for(int i = 0;i < k;i++){
ans -= of[i];
}
cout<<ans;
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL); cout.tie(NULL);
int t = 1;
while (t--) {
solve();
}
return 0;
}
