#include <bits/stdc++.h>
using namespace std;
#define int long long
#define el cout<<endl;
#define ff for(int i=0;i<n;i++)
#define fr(n,m) for(int i=n;i<m;i++)
#define frj(n,m) for(int j=n;j<m;j++)
#define frl(n,m) for(int l=n;l<m;l++)
#define frd(n,m) for(int d=n;d<m;d++)
#define mii map<int,int>
#define mci map<char,int>
#define vi vector<int>
#define vc vector<char>
#define pb push_back
#define als(z) cout<<z.fi<<" "<<z.se<<endl;
#define all(n) n.begin(),n.end()
#define rall(n) n.rbegin(),n.rend()
const int mod = 1e9 + 7;
// const int mod=998
int i = 0, j = 0, k = 0, l = 0, h = 0, w = 0, a = 0, b = 0, c = 0, d = 0, n = 0, m = 0;
int num = 0, ans = 0, sum = 0;
const int N = 1e3 + 5;
void solve() {
cin >> n >> k;
vi v(n);
ff{
cin >> v[i];
}
vi w;
fr(1, n) {
w.pb(v[i] - v[i - 1] - 1);
// cout << v[i] - v[i - 1] - 1 << " ";
}
sort(rall(w));
l = v[n - 1] + 1 - v[0];
// cout << v[n - 1] + 1 - v[0];
fr(0, k - 1) {
l -= w[i];
}
cout << l;
// el;
// for (auto z : w) cout << z << " ";
}
signed main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int T = 1;
// cin >> T;
while (T--) {
cout << fixed << setprecision(12); solve();
el;
} return 0;
}
