#3错了

#include<bits/stdc++.h>
using namespace std;
long long x,y;
int main()
{
	long long a,b,c;
	cin>>a>>b>>c;
	double k,z,sum=0;
	x=a*c;
	y=b*(a+c);
	z=3.14*c*c;
	z=z/4;
	sum=x+y+z;
	sum=sum/10000;
	cout<<fixed<<setprecision(3)<<sum<<endl;
	return 0;
}

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