#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
double c[10010];
const double pi=acos(-1);
inline int gl(int a)
{
	return a&(-a);
}
inline void gj(int a,double s)
{
	while(a<=10005)
	{
		if(c[a]<s)
		    c[a]=s;
		a+=gl(a);
	}
}
inline double gs(int a)
{
	double re=0.0;
	while(a)
	{
		if(re<c[a])
		    re=c[a];
		a-=gl(a);
	}
	return re;
}
int main()
{
	freopen("zootopia.in","r",stdin);
	freopen("zootopia.out","w",stdout);
	double pr=0.0;
	int n;
	scanf("%d",&n);
	while(n--)
	{
		int H,R;
		scanf("%d%d",&R,&H);
		double re=gs(10005-R-1);
		double r=(double)R,h=(double)H;
		re+=h*pi*r*r;
		if(pr<re)
		    pr=re;
		gj(10005-R,re);
	}
	printf("%.2lf",pr);
	getchar();
	getchar();
}