#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<int, pii> piii;
typedef pair<ll, ll> pll;
typedef pair<ll, pll> plll;
#define fi first
#define se second
const int INF = 1e9+1;
const int P = 1000000007;
const ll LLINF = (ll)1e18+1;
template <typename T>
ostream& operator<<(ostream& os, const vector<T>& v) { for(auto i : v) os << i << " "; os << "\n"; return os; }
template <typename T1, typename T2>
ostream& operator<<(ostream& os, const pair<T1, T2>& p) { os << p.fi << " " << p.se; return os; }
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
#define rnd(x, y) uniform_int_distribution<int>(x, y)(rng)
ll mod(ll a, ll b) { return ((a%b) + b) % b; }
ll ext_gcd(ll a, ll b, ll &x, ll &y) {
ll g = a; x = 1, y = 0;
if(b) g = ext_gcd(b, a % b, y, x), y -= a / b * x;
return g;
}
ll inv(ll a, ll m) {
ll x, y; ll g = ext_gcd(a, m, x, y);
if(g > 1) return -1;
return mod(x, m);
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n, k; cin >> n >> k;
vector<int> A(n);
for(auto &i : A) cin >> i;
vector<int> B;
for(int i = 1; i < n; i++) B.push_back(A[i]-A[i-1]-1);
sort(B.begin(), B.end(), greater<int>());
int ans = 1+A.back()-A.front();
for(int i = 0; i < k-1; i++) ans -= B[i];
cout << ans << "\n";
return 0;
}
