#include <bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define FOR(i,a,b) for (auto i = (a); i <= (b); ++i)
#define NFOR(i,a,b) for(auto i = (a); i >= (b); --i)
#define all(x) (x).begin(), (x).end()
#define sz(x) int(x.size())
#define mp(i,a) make_pair(i,a)
#define pb(a) push_back(a)
#define bit(x,b) (x&(1LL<<b))
typedef long long int lli;
typedef pair <lli,lli> ii;
typedef pair <lli,ii> iii;
typedef vector <lli> vi;
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int test=1;
for(;test>0;--test)
{
lli n;
double ans=0;
cin>>n;
int k=-1;
vector<double> f(n),s(n);
for(int i=0;i<n;++i)
cin>>f[i]>>s[i];
sort(all(f),greater<double>());
sort(all(s),greater<double>());
if(k==-1&&s[0]<1)
k=0;
for(int i=1;i<n;++i)
{
if(k==-1&&s[i]<1)
k=i;
f[i]=f[i]+f[i-1];
s[i]=s[i]+s[i-1];
}
if(k==-1)
k=n-1;
for(int i=0;i<n;++i)
{
lli j=lower_bound(all(s),f[i])-s.begin();
ans=max(ans,min(f[i]-i-1-min(n-1,j)-1,s[min(j,n-1)]-i-1-min(j,n-1)-1));
j=min(j-1,k*1LL);
ans=max(ans,min(f[i]-i-1-j-1,s[j]-i-1-j-1));
}
cout<<fixed<<setprecision(4)<<ans<<endl;
}
return(0);
}
