#include "bits/stdc++.h"
#define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define ll long long
#define pb push_back
#define in insert
#define F first
#define S second
#define vll vector<ll>
#define all(v) v.begin(),v.end()
#define endl '\n'
#define pii pair<ll,ll>
#define yes cout << "YES" << endl;
#define no cout << "NO" << endl;
using namespace std;
const ll INF = 1e18, mod = 1e9 + 7, N = 2e5 + 5;
ll gcd(ll a, ll b){
if(b == 0){
return a;
}
return gcd(b, a%b);
}
ll lcm(ll a, ll b){
return (a / gcd(a,b)) * b;
}
void solve(){
ll n,m;
cin >> n >> m;
m--;
ll a[n];
for(int i = 0; i < n;i ++){
cin >> a[i];
}
ll sum = 0;
vector<ll>v;
for(int i = 0; i < n - 1; i++){
v.pb(a[i + 1] - a[i] - 1);
sum += a[i + 1] - a[i] - 1;
}
sort(all(v));
reverse(all(v));
for(int i = 0; i < m; i++){
sum -= v[i];
}
cout << sum + n << endl;
}
int main() {
fast;
ll t = 1;
// cin >> t;
while(t--){
solve();
}
return 0;
}
