30pts求助

#include <bits/stdc++.h>
#define int long long 
using namespace std;
int a[1000010];
int n,m;
bool check(int k)
{
	int sum=0;
	for(int i=1;i<=k;i++)
	{
		if(a[i]<k) continue;
		sum+=a[i]-k;
	}
	if(m<=sum) return 1;
	return 0;
}
signed main()
{
	cin>>n>>m;
	for(int i=1;i<=n;i++)
	cin>>a[i];
	sort(a+1,a+1+n);
	int l=0,r=a[n];
	int ans;
	while(l<=r)
	{
		int mid=(l+r)/2;
		if(check(mid)) l=mid+1,ans=mid;
		else r=mid-1;
	}
	cout<<ans;
    return 0;
}