519

#include <iostream>
#include <string>
#include <vector>
#include <cstdlib>
#include <deque>
#include <cmath>
#include <iomanip>
#include <algorithm>

using namespace std;
typedef pair<int, int> pii;
typedef pair<double, double> pdd;
typedef long long li;
typedef long double ld;
#define forn(i,n) for(int (i) = 0; (i) < n; ++(i))
#define EPS 1e-18

bool zero(double x) {
	return abs(x) < EPS;
}

const double INF = 1e19;

struct tp {
	int x, v;
};

bool operator < (const tp &a, const tp &b) {
	return a.x < b.x;
}

tp p[500500];
int n;

inline bool equal(double a, double b) {
	return b - a > -EPS;
}

bool f(double mid) {
	bool result = false;
	double maxx = -INF;
	for (int i = 0; i < n; i++) {
		double cur = (double)p[i].v * mid + p[i].x;
		if (p[i].v < 0) {
			if (equal(cur, maxx)) {
				result = true;
				break;
			}
			continue;
		}
		maxx = max(maxx, cur);
	}
	return result;
}

int main() {
#ifdef _DEBUG
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
#endif
	scanf("%d", &n);
	for (int i = 0; i < n; ++i)
		scanf("%d %d", &p[i].x, &p[i].v);

	sort(p, p + n);
	double ans = -1;
	double l = 0, r = 2e9;
	for (int i = 0; i < 100; ++i) {
		double mid = (l + r) / 2;

		if (f(mid))
			ans = mid, r = mid;
		else
			l = mid;
	}
	printf("%.18lf\n", ans);

	return 0;
}