#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i,a,b) for (int i = a; i <= b; i++)
#define per(i,a,b) for (int i = a; i >= b; i--)
#define pii pair<int,int>
#define fi first
#define se second
#define endl '\n'
#define pb push_back
#define all(v) (v).begin(), (v).end()
const int MAXN = 5e5+10;
const int INF = 1e18+10;
const int MOD = 1e9+7;
float a[MAXN], b[MAXN];
void solve() {
int n; cin >> n;
rep(i,1,n) {
cin >> a[i] >> b[i];
}
sort(a+1,a+n+1, greater<float>());
sort(b+1,b+n+1, greater<float>());
rep(i,1,n) a[i] += a[i-1];
rep(i,1,n) b[i] += b[i-1];
float ans = 0;
rep(x,1,n) {
rep(y,1,n) {
float x1 = a[x],x2 = b[y];
ans = max(ans,min(x2, x1)-x-y);
}
}
cout << fixed << setprecision(4) << ans << endl;
}
int32_t main() {
ios_base::sync_with_stdio(0);cin.tie(nullptr);
int tt = 1;
//cin >> tt;
while(tt--) solve();
}
