Submission #6485243

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Source Code Expand

#include <bits/stdc++.h>
 
using namespace std;
 
#define ll long long int
#define mod 1000000007
 
#define REP(i, n) for(int i = 0; i < (n); i++)
#define NREP(i, n) for(int i = 1; i <= (n); i++)
#define SREP(i, s) for(int i = 0; i < (s.size()); i++)
#define SORT(v, n) sort(v, v+n);
#define GSORT(v, n) sort(v, v+n, greater<int>());
#define VSORT(v) sort(v.begin(),v.end());
#define VGSORT(v) sort(v.begin(),v.end(),greater<int>());
#define REV(a) reverse(begin(a),end(a));

int main(){
	ios::sync_with_stdio(false);cin.tie(0);
	cout << fixed << setprecision(20);
////////////////////////////////////////////
	int n;
	cin >> n;
	int r[n];
	double ans=0;
	REP(i,n) cin >> r[i];
	GSORT(r,n);
	REP(i,n){
		if(i%2==0){
			ans+=pow(r[i],2);
		}else{
			ans-=pow(r[i],2);
		}
	}
	cout << ans*M_PI << endl;
///////////////////////////////////////////
}

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