codeforces D Salary Changing

#include<cstdio>
#include<cstring>
#include<queue>
#include<cmath>
#include<algorithm>
#include<map>
#include<vector>
#include<string>
#include<set>
#define ll long long
using namespace std;
int l[500010];
int r[500010];
int n;
ll s;
int check(int md)
{
    int k=(n+1)/2;
    vector<int> M;
    for(int i=1;i<=n;i++)
    {
        int v=max(l[i],md);
        if(r[i]<v) continue;
        M.push_back(v-l[i]);
    }
    if((int)M.size()<k)
        return 0;
    ll sum=0;
    sort(M.begin(),M.end());
    for(int i=0;i<k;i++)
        sum+=M[i];
    return sum<=s;
}
int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {

        scanf("%d%lld",&n,&s);
        for(int i=1;i<=n;i++)
        {
            scanf("%d%d",&l[i],&r[i]);
            s-=l[i];
        }
        int st=0,ed=1e9;
        while(st<ed)
        {
            int md=(st+ed+1)/2;
            if(check(md))
            {
                st=md;
            }
            else
                ed=md-1;
        }
        printf("%d\n",st);
    }
}