#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC target("avx2,fma")
#define rep(i,l,r) for (int i = l; i < r; i++)
#define repr(i,r,l) for (int i = r; i >= l; i--)
#define X first
#define Y second
#define pb push_back
#define endl '\n'
#define debug(x) cerr << #x << " : " << x << endl;
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pll;
const long long int N = 1e5+20,mod = 1e9+7,inf = 1e9+10,sq = 400;
inline int mkay(int a,int b){
if (a+b >= mod) return a+b-mod;
if (a+b < 0) return a+b+mod;
return a+b;
}
inline int poww(int n,int k){
int c = 1;
while (k){
if (k&1) c = (1ll*c*n)%mod;
n = (1ll*n*n)%mod;
k >>= 1;
}
return c;
}
ld a[N],b[N];
ld suf[N][2];
int n;
inline ld check(int i){
if (i > n || i < 0) return 0;
ld ans = min(suf[n-i][0]-i,ld(0));
rep(j,1,n+1){
ans = max(ans,min(suf[n-i][0],suf[n-j][1])-i-j);
}
return ans;
}
inline ld ternery(){
int l = 0,r = n,m1 = 9,m2 = 0;
while (r-l > 2){
m1 = (2*l+r)/3;
m2 = (l+2*r)/3;
if (check(m1) < check(m2)) l = m1;
else r = m2;
}
ld ans = max(check(0),check(n));
rep(i,-300,300) ans = max(check(l+i),ans);
return ans;
}
int main(){
ios :: sync_with_stdio(0); cin.tie(0);
cin >> n;
rep(i,0,n){
cin >> a[i] >> b[i];
}
sort(a,a+n);
sort(b,b+n);
repr(i,n-1,0){
suf[i][0] = suf[i+1][0]+a[i];
suf[i][1] = suf[i+1][1]+b[i];
}
cout << setprecision(4) << fixed << max(ld(0),ternery()) << endl;
}
