Language: C++

#include "bits/stdc++.h"
using namespace std;
#define ll long long
#define endl '\n'
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define rep2(i,a,b) for(int i=int(a);i<int(b);i++)
#define pb emplace_back
#define all(x) (x).begin(),(x).end()
ll mod=1e9+7;
ll mod2=998244353;
const int INF=1e9;


signed main() {
	ll n,d;
	cin>>n>>d;
	ll d=d*2+1;
	ll ans=n/d;
	if(n%d!=0)ans++;
	cout<<ans<<endl;
}


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Compiler output:
a.cc: In function 'int main()':
a.cc:17:12: error: redeclaration of 'long long int d'
   17 |         ll d=d*2+1;
      |            ^
a.cc:15:14: note: 'long long int d' previously declared here
   15 |         ll n,d;
      |              ^