#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define mod 1000000007
#define h1 7897897897897897
#define h2 7897466719774591
#define b1 98762051
#define b2 98765431
#define inf 1000000000
#define pi 3.1415926535897932384626
#define LMAX 9223372036854775807
#define ll long long
#define fi first
#define se second
#define pii pair<int, int>
#define pll pair<ll, ll>
#define vi vector<int>
#define vl vector<ll>
#define vp vector<pii>
#define SET(a, b) memset(a, b, sizeof(a));
#define all(x) (x).begin(), (x).end()
#define flush fflush(stdout)
#define debug printf("Hello\n")
#define FOR(i, a, b) for (int i = (a); i <= (b); i++)
#define FORD(i, a, b) for (int i = (a); i >= (b); i--)
//priority_queue <int, vector <int>, greater <int> > pq;
int n, m, k, x, y, sum, cnt, ans, a[100005], b[100005];
int main () {
ios::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
cin >> n >> k;
FOR(i, 1, n) {
cin >> a[i];
}
FOR(i, 1, n-1) {
b[i] = a[i+1] - a[i] - 1;
}
ans = a[n] + 1 - a[1];
sort(b+1, b+n);
reverse(b+1, b+n);
FOR(i, 1, k-1) {
ans -= b[i];
}
cout << ans << endl;
return 0;
}
