#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define el '\n'
#define pb push_back
#define mp make_pair
#define niggers \
ios_base::sync_with_stdio(false); \
cin.tie(NULL); \
cout.tie(NULL);
#define file(name) \
freopen(name ".inp", "r", stdin); \
freopen(name ".out", "w", stdout);
typedef long long ll;
typedef pair<long long, long long> pll;
typedef pair<int, int> pii;
typedef vector<long long> vll;
typedef vector<int> vi;
const ll MOD = 1e9 + 7;
const int inf = 1e9;
const int mxN = 1e2 + 5;
const int mxM = 1e3 + 5;
const int N = 2e5 + 5;
int hx[] = {-1, 0, 1, 0};
int hy[] = {0, 1, 0, -1};
long double a[N], b[N], psa[N], psb[N];
;
int main()
{
// freopen("b.inp", "r", stdin);
// freopen("b.out", "w", stdout);
ll pinkkiu = 1;
// cin >> pinkkiu;
while (pinkkiu--)
{
ll n;
cin >> n;
for (int i = 1; i <= n; ++i)
{
cin >> a[i] >> b[i];
}
sort(a + 1, a + n + 1, greater<>());
sort(b + 1, b + n + 1, greater<>());
for (int i = 1; i <= n; ++i)
{
psa[i] = psa[i - 1] + a[i];
psb[i] = psb[i - 1] + b[i];
}
// for(int i = 1;i <= n ; ++i){
// cout << psa[i] << ' ' << psb[i] << endl;
// }
long double ans = 0;
for (int i = 1; i <= n; ++i)
{
// cout << psa[i] << ' ' << psb[i] << endl;
int l = 1, r = n;
ll pos = -1;
while (l <= r)
{
int mid = l + r >> 1;
if (psb[mid] >= psa[i])
{
r = mid - 1;
pos = mid;
}
else
{
l = mid + 1;
}
}
// cout << pos << ' ';
if (pos != -1)
{
ans = max(ans, psa[i] - (1.0) * i - 1.0 * pos);
// cerr << ans << ' ';
}
}
for (int i = 1; i <= n; ++i)
{
int l = 1, r = n;
ll pos = -1;
while (l <= r)
{
int mid = l + r >> 1;
if (psa[mid] >= psb[i])
{
r = mid - 1;
pos = mid;
}
else
{
l = mid + 1;
}
}
if (pos != -1)
{
ans = max(ans, psb[i] - 1.0 * i - 1.0 * pos);
}
}
cout << fixed << setprecision(4) << ans;
}
}
