#include <bits/stdc++.h>
#define ll long long
#define fi first
#define se second
#define endl '\n'
#define MASK(i) (1LL << (i))
#define ull unsigned long long
#define ld long double
#define pb push_back
#define all(x) (x).begin() , (x).end()
#define BIT(x , i) ((x >> (i)) & 1)
#define TASK "task"
#define sz(s) (int) (s).size()
using namespace std;
const int mxN = 3e5 + 227;
const int inf = 1e9 + 277;
const int mod = 24211007;
const ll infll = 1e18 + 7;
const int base = 307;
const int LOG = 20;
template <typename T1, typename T2> bool minimize(T1 &a, T2 b) {
if (a > b) {a = b; return true;} return false;
}
template <typename T1, typename T2> bool maximize(T1 &a, T2 b) {
if (a < b) {a = b; return true;} return false;
}
int n;
double a[mxN];
double b[mxN];
void solve()
{
cin >> n;
for(int i = 1; i <= n; i++) cin >> a[i] >> b[i];
sort(a + 1, a + 1 + n, greater<double>());
sort(b + 1, b + 1 + n, greater<double>());
double s1 = 0, s2 = 0;
double res = 0;
int pos = 1;
for(int i = 1; i <= n; i++) {
s1 += a[i];
while(pos <= n && min(s1 - i - pos + 1, s2 - i - pos + 1) <= min(s1 - i - pos, s2 - i - pos + b[pos])) {
s2 += b[pos];
++pos;
}
maximize(res, min(s1 - i - pos + 1, s2 - i - pos + 1));
}
cout << fixed << setprecision(4) << res;
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
//freopen(TASK".in" , "r" , stdin);
//freopen(TASK".out" , "w" , stdout);
int tc = 1;
// cin >> tc;
while(tc--) {
solve();
}
return 0;
}
