#include <bits/stdc++.h>
using namespace std;
#ifdef DEBUG
#include "../Library/debug.h"
#else
#define dbg(x...)
#endif
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef vector<int> vi;
typedef vector<bool> vb;
typedef vector<ll> vl;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define F0R(i, a) for (int i = 0; i < (a); ++i)
#define FORd(i, a, b) for (int i = (b) - 1; i >= (a); --i)
#define F0Rd(i, a) for (int i = (a) - 1; i >= 0; --i)
#define trav(a, x) for (auto& a : x)
#define f first
#define s second
#define pb push_back
#define sz(x) (int)(x).size()
#define all(x) x.begin(), x.end()
const char nl = '\n';
const int INF = 1e9;
const int MOD = 1e9 + 7;
void solve(){
int n;
cin>>n;
vector<double> a(n),b(n);
F0R(i,n){
cin>>a[i]>>b[i];
a[i]--; b[i]--;
}
sort(all(a),[](auto& i, auto& j){return i>j;});
sort(all(b),[](auto& i, auto& j){return i>j;});
F0R(i,n-1)
b[i+1]+=b[i];
pair<double,double> ans={0,0};
double x=0;
auto f=[&](int i,int j){
return min(x-(j+1),b[j]-(i+1));
};
F0R(i,n){
x+=a[i];
int l=-1,r=n;
while(r-l>1){
int mid=(r+l)>>1;
if(f(i,mid)>f(i,mid+1)){
r=mid;
}
else{
l=mid;
}
}
l++;
if(min(x-(l+1),b[l]-(i+1))>min(ans.f,ans.s))
ans={x-(l+1),b[l]-(i+1)};
}
cout<<fixed<<setprecision(4)<<min(ans.f,ans.s)<<nl;
}
int32_t main(){
ios::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
int TC = 1;
// cin >> TC;
while(TC--){
solve();
}
return 0;
}
