Submission #1533900

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Source Code Expand

#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>
#include <iomanip>

using namespace std;

const double PI=3.14159265358979;

int main(){
    int n=0;
    vector<int> data;
    double res=0;
    cin >> n;
    for(int i=0;i<n;i++){
        int temp=0;
        cin >> temp;
        data.push_back(temp*temp);
    }
    sort(data.begin(),data.end(),greater<int>());
    int mul=1;
    for(int i=0;i<n;i++){
        res+=(data[i]*mul);
        mul*=-1;
    }
    res*=PI;
    cout << fixed;
    cout << setprecision(8) << res << endl;
    return 0;
}

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