请问为什么代码跑的结果永远比真实结果大1？求助

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;

LL N, M;
LL tree[1000010];

bool check(LL x)  //x为二分的最大高度
{
    LL k = 0, sum = 0; //分别记录砍树的数量和总长度
    for (int i = 0; i < N; i++)
    {
        if (tree[i] > x)
        sum += tree[i] - x;
    }
    if (sum >= M) return true;    //锯片的高度太低了
    else return false;    //锯片的高度太高了
}

LL bs(LL left, LL right)
{
    LL mid;
    while (left <= right)
    {
        mid = left + right >> 1;
        if (check(mid))  left = mid + 1;
        else right = mid - 1;
    }
    return left;
}

int main()
{
    scanf("%lld %lld", &N, &M);
    for (int i = 0; i < N; i++) scanf("%lld", &tree[i]);
    LL ans = bs(0, 2e9+1);
    printf("%lld", ans-1);

    return 0;
}