带权中位数，百度百科可以看http://baike.baidu.com/view/1209446.htm
/* From: Lich_Amnesia
* Time: 2014-01-06 20:04:54
*
* SGU 114 带权中位数
* */
#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <queue>
#include <set>
#include <vector>
using namespace std;
const int INF = ~0u>>1;
typedef pair <int,int> P;
#define MID(x,y) ((x+y)>>1)
#define iabs(x) ((x)>0?(x):-(x))
#define REP(i,a,b) for(int i=(a);i<(b);i++)
#define FOR(i,a,b) for(int i=(a);i<=(b);i++)
#define pb push_back
#define mp make_pair
#define print() cout<<"——–"<<endl
#define maxn 15100
struct node{
double pos;
int num;
}p[maxn];
bool cmp(node a,node b){
return a.pos < b.pos;
}
int main(){
int n;
int tot = 0;
cin >> n;
for (int i = 0; i < n; i ++){
scanf("%lf%d",&p[i].pos, &p[i].num);
tot += p[i].num;
}
sort(p, p + n, cmp);
++tot /= 2;
int t = 0;
for (int i = 0; i < n; i ++){
t += p[i].num;
if (t >= tot) {
printf("%.5fn", p[i].pos);
break;
}
}
return 0;
}