#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;
double 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<double>());
sort(b+1,b+n+1, greater<double>());
rep(i,1,n) a[i] += a[i-1];
rep(i,1,n) b[i] += b[i-1];
double ans = 0;
priority_queue<double> pq;
int j = 1;
rep(x,1,n) {
while (j<=n && b[j]<=a[x]) {
pq.push(b[j]-j);
j++;
}
if(pq.size()>0) ans = max(ans, pq.top()-x);
if(j<=n) ans = max(ans, a[x]-x-j);
}
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();
}
