Problem:
Score : 100 points

Problem Statement

Print the circumference of a circle of radius R.

Constraints

1 \leq R \leq 100

All values in input are integers.

Input

Input is given from Standard Input in the following format:

R

Output

Print the circumference of the circle.
Your output is considered correct if and only if its absolute or relative error from our answer is at most 10^{-2}.

Sample Input 1

1

Sample Output 1

6.28318530717958623200

Since we accept an absolute or relative error of at most 10^{-2}, 6.28 is also an acceptable output, but 6 is not.

Sample Input 2

73

Sample Output 2

458.67252742410977361942

Solution in C++ (GCC 9.2.1) (judge verdict: Accepted)

/*
    Author: Alam Khan
    AUST CSE 40th Batch

*/

#include<bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/detail/standard_policies.hpp>
using namespace __gnu_pbds;

typedef long long ll;
typedef pair<ll,ll> pll;
typedef vector<ll> vl;
typedef deque<ll> dl;
typedef stack<ll> stl;
typedef set<ll> sl;
typedef map<string, ll> msl;
typedef map<ll,ll> mll;
typedef tree<ll,null_type,less_equal<ll>,rb_tree_tag,tree_order_statistics_node_update>ordered_set;
#define sf(n)     scanf("%lld",&n)
#define sff(n,m)     scanf("%lld %lld",&n,&m)
#define sfff(n,m,r)     scanf("%lld %lld %lld",&n,&m,&r)
#define sfs(n)     scanf("%s",n)
#define pf(n)     printf("%lld\n",n)
#define pff(n,m)     printf("%lld %lld\n",n,m)
#define pfff(n,m,r)     printf("%lld %lld %lld\n",n,m,r)
#define pfs(n)     printf("%s\n",n)
#define pfcs(i,n)     printf("Case %lld: %lld\n",i,n)
#define pb     push_back
#define prf     printf
#define inf     2e18
#define low     -1000000000000
#define PI        acos(-1.0)
#define rep1(i,n) for(i=1;i<n;i++)
#define rep0(i,n) for(i=0;i<n;i++)
#define rep(i,a,n) for(i=a;i<n;i++)
#define repe1(i,n) for(i=1;i<=n;i++)
#define repe0(i,n) for(i=0;i<=n;i++)
#define repe(i,a,n) for(i=a;i<=n;i++)
#define endl  "\n"
#define FAST  ios_base::sync_with_stdio(false);cin.tie(NULL);
#define fr freopen("input.txt","r",stdin)
#define fw freopen("output.txt","w",stdout)

int main()
{
    double r;
    cin>>r;
    r = 2*PI*r;
    printf("%.9lf\n",r);
    return 0;
}