/*
ID: noszaly1
TASK: {TASK}
LANG: C++11
*/
//Noszály Áron 10o Debreceni Fazekas Mihály Gimnázium
#include<iostream>
#include<vector>
#include<map>
#include<set>
#include<cassert>
#include<cassert>
#include<unordered_map>
#include<unordered_set>
#include<functional>
#include<queue>
#include<stack>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<sstream>
#include<iomanip>
#include<cstdio>
#include<cstdlib>
#include<numeric>
using namespace std;
#define all(x) (x).begin(), (x).end()
#define pb push_back
#define xx first
#define yy second
#define sz(x) (int)(x).size()
#define gc getchar
#define IO ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#define mp make_pair
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
const double PI=acos(-1);
template<typename T> T getint() {
T val=0;
char c;
bool neg=false;
while((c=gc()) && !(c>='0' && c<='9')) {
neg|=c=='-';
}
do {
val=(val*10)+c-'0';
} while((c=gc()) && (c>='0' && c<='9'));
return val*(neg?-1:1);
}
int main() {
IO;
int n;
cin>>n;
vector<double> a,b;
for(int i=0;i<n;++i) {
double x,y;cin>>x>>y;
a.pb(x);
b.pb(y);
}
sort(all(a));
sort(all(b));
reverse(all(a));
reverse(all(b));
int L=-1, R=-1;
double s1=0,s2=0;
double ans=0.0;
while(L<n || R<n) {
//cerr<<L<<" "<<R<<" "<<s1<<" "<<s2<<"\n";
if((s1<s2 && L<n) || (R==n)) {
s1+=a[++L]-1;
s2-=1;
ans=max(ans, min(s1, s2));
}else {
s2+=b[++R]-1;
s1-=1;
ans=max(ans, min(s1, s2));
}
}
cout<<fixed<<setprecision(4)<<ans<<"\n";
return 0;
}
