using namespace std;
#include <bits/stdc++.h>
typedef long long int ll;
typedef unsigned long long int ull;
typedef pair<int,int> ii;
typedef pair<ll,ll> dl;
typedef vector<ii> vii;
typedef vector<dl> vdll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<string> vs;
#define pb push_back
#define mp make_pair
#define ft first
#define sc second
#define in insert
#define bs binary_search
#define INF LLONG_MAX
#define rc(s) return cout << s,0
#define int ll
const ll mod=1e9+7;
const int N=100005;
#define int ll
/*----------------------------*/
/*----------------------------*/
int32_t main() {
//freopen("sol.in","r",stdin);
//freopen("sol.out","w",stdout);
/**///------------------------///**/
/**/ios::sync_with_stdio(false);/**/
/**///------------------------///**/
int n;
cin>>n;
double a,b;
vector<double> x,y;
for(int i=1;i<=n;i++)cin>>a>>b,x.pb(a),y.pb(b);
sort(x.begin(),x.end());
sort(y.begin(),y.end());
reverse(x.begin(),x.end());
reverse(y.begin(),y.end());
double ans=0;
double inda=0,indb=0;
a=0,b=0;
while(inda<=n&&indb<=n)
{
if(a<b&&inda<n)
{
a+=x[inda];
inda++;
}
else
{
b+=y[indb];
indb++;
}
//cout<<inda<<' '<<indb<<endl;
ans=max(ans,min(a-inda-indb,b-inda-indb));
}
printf("%.4lf",(double)ans);
//THIS IS IS THE END
}
