#include<iostream>
#include<algorithm>
#include<iomanip>
using namespace std;

const int MAXN = 1e5 + 5;
double a[MAXN], b[MAXN];
double suma[MAXN], sumb[MAXN];
int n;

int main(){
    freopen("wager.in", "r", stdin);
    freopen("wager.out", "w", stdout);
    ios::sync_with_stdio(0);
    cin.tie(0);
    cin >> n;
    for(int i = 1;i <= n;i ++){
        cin >> a[i] >> b[i];
    }
    sort(a + 1, a + n + 1, [](double& x, double& y){
        return x > y;
    });
    sort(b + 1, b + n + 1, [](double& x, double& y){
        return x > y;
    });
    for(int i = 1;i <= n;i ++){
        suma[i] = suma[i - 1] + a[i];
        sumb[i] = sumb[i - 1] + b[i];
    }
    double ans = 0.0;
    int i = 1,j = 1;
    while(i <= n && j <= n){
        if(suma[i] > sumb[j]){
            ans = max(ans, sumb[j] - i - j);
            j ++;
        }
        else{
            ans = max(ans, suma[i] - i - j);
            i ++;
        }
    }
    cout << fixed << setprecision(4) << ans << '\n';
    // cerr << "Time : " << 1.0 * clock() / CLOCKS_PER_SEC << "s \n";
    return 0;
}