AC了，但有一点疑惑

#include<bits/stdc++.h>
#define int long long
#define N 1000010

using namespace std;

int read()
{
    int x = 0,f = 1;
    char c = getchar();
    while(c<'0' || c>'9')
	{
        if(c=='-') f = -1;
        c = getchar();
    }
    while(c>='0' && c<='9')
	{
        x = (x<<3)+(x<<1)+(c^48);
        c = getchar();
    }
    return x*f;
}

int a[N],n,m;

int check(int h)
{
	int ans=0;
	for (int i=1;i<=n;i++)
		if (a[i]>h) ans += a[i]-h;
	return ans;
}

signed main()
{
	n=read(),m=read();
	int maxn = 0;
	for (int i=1;i<=n;i++)
	{
		a[i]=read();
		maxn = max(maxn,a[i]);
	}
	int l=1,r=maxn,ans=0;
	while(l+1<r)
	{
		int mid = (l+r)>>1,k = check(mid);
		if (k>=m)
		{
			ans = min(ans,mid);
			l = mid;
		}
		else r = mid;
	}
	cout << l << endl;
	return 0; 
}

while(l+1<r)