#include<bits/stdc++.h>
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
typedef long long ll;
#define int ll
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define pb push_back
#define all(x) x.begin(), x.end()
#define sz(x) (int)x.size()
#define mispertion ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0)
#define F first
#define S second
#define getlast(s) (*s.rbegin())
#define debg cout << "OK\n"
const ld PI = 3.1415926535;
const int N = 100000+1;
const int M = 7e6 + 1;
int mod = 998244353;
const int infi = INT_MAX;
const ll infl = LLONG_MAX;
const int P = 31;
int mult(int a, int b) {
return a * 1LL * b % mod;
}
int sum(int a, int b) {
if (a + b < 0)
return a + b + mod;
if (a + b >= mod)
return a + b - mod;
return a + b;
}
ll binpow(ll a, ll n) {
if (n == 0)
return 1;
if (n % 2 == 1) {
return binpow(a, n - 1) * a % mod;
} else {
ll b = binpow(a, n / 2);
return b * b % mod;
}
}
int a[N];
void solve(){
int n, k;
cin >> n >> k;
vector<int> v = {};
int ans = 0;
for(int i = 1; i <= n; i++){
cin >> a[i];
if(i > 1)
v.pb(a[i] - a[i - 1] - 1);
}
ans = a[n] - a[1] + 1;
sort(all(v));
reverse(all(v));
for(int i = 0; i < k - 1; i++){
ans -= v[i];
}
cout << ans << '\n';
}
signed main() {
mispertion;
int t = 1;
//cin >> t;
while(t--){
solve();
}
return 0;
}
