#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define vll vector<ll>
#define vbool vector<bool>
#define pairll pair<ll, ll>
#define pb push_back
#define fi first
#define sc second
const ll md = 1e9+7;
void solve(){
ll n, k; cin >> n >> k;
vll a(n); for(ll i = 0; i < n; i++) cin >> a[i];
ll res = a[n-1] - a[0] +1;
vll gap;
for(ll i = 1; i < n; i++){
gap.pb(a[i] - a[i-1] - 1);
}
sort(gap.begin(), gap.end(), greater<ll>());
for(ll i = 0; i < k-1; i++){
res -= gap[i];
}cout << res << endl;
}
int main(){
ll t = 1; //cin >> t;
while(t--)solve();
}
