#include<iostream>
#include<cstdio>
#include<stdio.h>
#include<cstring>
#include<string>
#include<iomanip>
#include<algorithm>
#include<cmath>
#include<vector>
#include<utility>
#include<bitset>
#include<list>
#include<set>
#include<queue>
#include<map>
#include<stack>
#include<ctime>
#include<random>
using namespace std;
typedef unsigned int uint;
typedef long long ll;
typedef unsigned long long ull;
const ll MAXN=5*1e6+2;
const ll inf=0x3f3f3f3f;
double eps=1e-11;
struct node{
    int x,y;
}a[MAXN];
int n;
double ans;
bool check(double c){
    double tmp=a[1].x;
    if(tmp>c){
        return false;
    }
    double last=a[1].y-a[1].x;
    for(int i=2;i<=n;i++){
        if(a[i].x<=last){
            double num=min(last-a[i].x,c);
            last=a[i].y+num;
        }
        else{
            if(a[i].x-last>c){
                return false;
            }
            last=a[i].y-(a[i].x-last);
        }
    }
    if(last>=10000){
        return true;
    }
    else{
        return false;
    }
}
bool cmp(const node &x,const node &y){
    if(x.x==y.x){
        return x.y<y.y;
    }
    else{
        return x.x<y.x;
    }
}
int main(){
    cin>>n;
    for(int i=1;i<=n;i++){
        cin>>a[i].x>>a[i].y;
    }
    sort(a+1,a+n+1,cmp);
    double l=0;
    double r=1e17;
    while(r-l>=eps){
        double mid=(l+r)/2;
        if(check(mid)){
            r=mid;
            ans=mid;
        }
        else{
            l=mid;
        }
    }
    cout<<ans<<endl;
    return 0;
}