#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef long double ld;
#define pb push_back
#define pf push_front
#define fi first
#define se second
const ll mod = 1e9+7;
signed main()
{
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
// freopen("test.inp","r",stdin); freopen("test.out","w",stdout); freopen("test.err","w",stderr);
ll n, k; cin >> n >> k; k--;
vector<ll> v, a(n);
for (ll i = 0; i < n; i++) cin >> a[i];
for (ll i = 1; i < n; i++) v.pb(a[i]-a[i-1]-1);
ll ans = a[n-1]-a[0]+1;
sort(v.begin(),v.end());
while (k--) {ans -= v.back(); v.pop_back();}
cout << ans;
}
