#include <bits/stdc++.h>
using namespace std;
#define double long double
double tree[100009]={0.0};
#define PI acos(-1)
int n;
vector<double> v,p;
void update(int idx,double val)
{
	for(;idx<=100006;idx+=idx&-idx)
		tree[idx]=max(tree[idx],val);
}
double read(int idx)
{
	double s=0;
	for(;idx>0;idx-=idx&-idx)s=max(s,tree[idx]);
	return s;
}
int main() 
{
	cin>>n;
	v.push_back(-1.0);
	p.push_back(-1.0);
	for(int i=1;i<=n;i++)
	{
		long long r,h;
		cin>>r>>h;
		v.push_back((double)h*r*r*PI);
		p.push_back((double)h*r*r*PI);
	}
	//v.push_back(-1.0);
	sort(v.begin(),v.end());
	for(int i=1;i<=n;i++)
	{
		int t=(int)(upper_bound(v.begin(),v.end(),p[i])-v.begin());
		double a=read(t-1)+p[i];
		update(t,a);
	}
	double ans=0.0;
	for(int i=1;i<=100006;i++)
		ans=max(ans,read(i));
	printf("%0.14Lf\n",ans);
	return 0;
}

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40 10