WA*27，样例全过

#include<cstdio>
#include<algorithm>
using namespace std;
const int N=5e5+10; int a[N]; bool used[N];
int main() {
  int n; scanf("%d",&n);
  for(int i=1;i<=n;i++) scanf("%d",&a[i]);
  int r=1,ans=0;
  for(int i=1;i<=n;i++) {
  	if(used[i]) continue;
  	while(r<=n&&a[r]<2*a[i]) r++;
  	if(r!=n+1) ans++,used[r++]=true;
  }
  printf("%d",ans);
  return 0;
}