#include<bits/stdc++.h>
#include<fstream>
using namespace std;
ifstream fin("FEEDING.INP");
ofstream fout("FEEDING.OUT");
#define sz(a) (int)a.size()
#define ll long long
#define pb push_back
#define forr(i, a, b) for(int i = a; i < b; i++)
#define dorr(i, a, b) for(int i = a; i >= b; i--)
#define ld long double
#define vt vector
#include<fstream>
#define fi first
#define se second
#define pll pair<ll, ll>
#define pii pair<int, int>
const ld PI = 3.14159265359;
using u128 = __uint128_t;
//const int x[4] = {1, -1, 0, 0};
// int y[4] = {0, 0, 1, -1};
const ll mod = 1e15 + 7, inf = 1e16;
const int mxn = 2e5 + 5;
int n, k;
ll a[mxn + 1];
signed main()
{
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> k;
for(int i = 1; i <= n; i++){
cin >> a[i];
}
vt<ll>seg;
for(int i = 1; i < n; i++){
seg.pb(a[i + 1] - a[i] - 1);
}
sort(seg.rbegin(), seg.rend());
ll ans = a[n] + 1 - a[1];
for(int i = 0; i < k - 1; i++){
ans -= seg[i];
}
cout << ans;
return(0);
}
