#include <bits/stdc++.h>
#define int int64_t
using namespace std;
signed main() { // they may not be all connected!!!
cin.tie(0);
ios_base::sync_with_stdio(0);
int n; cin >> n;
vector<double> bets1(n);
vector<double> bets2(n);
for (int i = 0; i<n; i++) {
cin >> bets1[i] >> bets2[i];
}
sort (bets1.begin(), bets1.end());
sort (bets2.begin(), bets2.end());
reverse(bets1.begin(), bets1.end());
reverse(bets2.begin(), bets2.end());
vector<double> pfs1={0}, pfs2={0};
for (int i = 0; i<n; i++) {
pfs1.push_back(pfs1.back()+bets1[i]);
pfs2.push_back(pfs2.back()+bets2[i]);
}
double res = 0;
double p1 = 1;
double p2 = 1;
res = max(res, min(pfs1[p1]-p1-p2, pfs2[p2]-p1-p2));
while (p1 < n || p2<n) {
if (p1==n) p2++;
else if (p2==n) p1++;
else if (pfs1[p1] <= pfs2[p2]) p1++; // better heuristic?
else p2++;
res = max(res, min(pfs1[p1]-p1-p2, pfs2[p2]-p1-p2));
}
printf("%.4lf\n",(double)res);
return 0;
}
