function - ans-1- circle area

#include<bits/stdc++.h>
using namespace    std;

#define flush                    cin.ignore(numeric_limits<streamsize>::max(),'\n')
#define FASTERIO                 ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define NL                       cout<<'\n';
#define pi                       acos(-1.0) //3.1415926535897932384626
#define pb                       push_back
#define mk                       make_pair
#define mx                       1000005
#define EPS                      1e-10
#define dpoint(x)                fixed<<setprecision(x)
# define my_sizeof(type) ((char *)(&type+1)-(char*)(&type))
typedef long long int            ll;
typedef double                   dl;
typedef unsigned long long int   ull;

dl area_of_circle(int radious){ //dl define as double in above of the code
  dl area = pi*radious*radious;
  return area;
}


int main() {

#ifdef anikakash
    clock_t tStart = clock();
    freopen("input.txt", "r", stdin);
    freopen("tmp.txt", "w", stdout);
#endif

    FASTERIO; //cmt when use scanf & printf ;

    int radious;
    cin>>radious;
    dl area = area_of_circle(radious);
    cout<<"area of the circle is : "<<area<<endl;

#ifdef anikakash
    fprintf(stderr, "\n>> Runtime: %.10fs\n", (double) (clock() - tStart) / CLOCKS_PER_SEC);
#endif

    return 0;
}