# include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef __int128 lll;
typedef vector<double> vd;
double solve(vd P)
{
	int n=P.size();
	if(n==2)
	{
		if(P[0]>P[1]) return 1;
		else if(P[0]<P[1]) return 0;
		else return 0.5;
	}
	double mx=-1;
	vector<int> pos;
	for(int i=0;i<n;i++)
		if(P[i]>mx) pos={i},mx=P[i];
		else if(P[i]==mx) pos.push_back(i);
	auto calc=[&](int i)
	{
		double minn=1;
		for(int j=1;j<n;j++)if(i!=j)
		{
			vd Q=P;
			double t=(1-P[i])/(1-P[j]-P[i]);
			for(int k=0;k<n;k++)
				if(k!=i) Q[k]*=t;
			Q.erase(Q.begin()+j);
			minn=min(minn,solve(Q));
		}
		return minn;
	};
	int sz=pos.size();
	if(P[0]<mx || sz==1) return calc(pos[0]);
	else return 1./sz*calc(0)+(sz-1.)/sz*calc(pos[1]);
}
ll exgcd(ll a,ll b,ll &x,ll &y)
{
	if(!b) return x=1,y=0,a;
	ll g=exgcd(b,a%b,y,x);
	y-=a/b*x;
	return g;
}
struct exCRT
{
	ll a,m;
	exCRT(ll _a=0,ll _m=0):a(_a),m(_m){}
	bool merge(const exCRT &C)
	{
		ll x,y,g=exgcd(m,C.m,x,y);
		if((a-C.a)%g) return false;
		m=m/g*C.m;
		a=(C.a+((a-C.a)/g*(lll)y%m+m)*C.m)%m;
		return true;
	}
}C(0,1);
int main()
{
	int T;
	ll a,m,n;
	cin>>T;
	while(T--)
	{
		scanf("%lld%lld",&a,&m);
		if(!C.merge(exCRT(a,m))) return puts("error"),0;
	}
	n=C.a;
	if(n>10) return puts("0.000000"),0;
	vd P(n,1./n);
	printf("%.6lf\n",solve(P));
	return 0;
}