Submission #1306735

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Source Code Expand

#include <iostream>
#include <math.h>
#include <stdio.h>
using namespace std;

int main(void){
	int n, i, sp = 0, tmp, rad[1000];
	bool swi = true;

	cin >> n;
	for(i=0; i<n; i++){
		cin >> rad[i];
	}

	for(i=0; i<n-1; i++){
		for(int j=i+1; j<n; j++){
			if(rad[i] > rad[j]){
				tmp = rad[i];
				rad[i] = rad[j];
				rad[j] = tmp;
			}
		}
	}

	//for(i=0; i<n; i++)
	//	cout << rad[i] << endl;

	for(i=n-1; i >= 0; i--){
		if(swi){
			sp += rad[i]*rad[i];
			swi=false;
		}else{
			sp -= rad[i]*rad[i];
			swi=true;
		}
	}

	printf("%.12f\n",(double)sp * M_PI);
}

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