#pragma GCC optimize("O2")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
#define ll long long int
#define F first
#define S second
#define pb push_back
const ll N = 1e5 + 10;
const ll LOG = 20;
const ll MOD = 1e9 + 7;
const ll INF = 1e9 + 10;
int n;
long double a[N], b[N], ans = 0;
long double f(int i, int j){
return min(a[i] - (long double)j, b[j] - (long double)i);
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n;
for(int i = 1; i <= n; i++){
cin >> a[i] >> b[i];
a[i] -= 1.0; b[i] -= 1.0;
}
sort(a + 1, a + n + 1);
reverse(a + 1, a + n + 1);
sort(b + 1, b + n + 1);
reverse(b + 1, b + n + 1);
for(int i = 1; i <= n; i++){
a[i] += a[i - 1];
b[i] += b[i - 1];
}
for (int i = 0; i <= n; i++){
int l = 0, r = n;
while (l + 1 <= r){
int mid = (l + r) / 2;
if (f(i, mid) < f(i, mid + 1)) l = mid + 1;
else r = mid;
}
ans = max(ans, f(i, r));
}
cout << fixed << setprecision(4) << ans << '\n';
return 0;
}
