
#include<bits/stdc++.h>
typedef long long ll;
typedef double ld;

void solve(){
    ll n;
    cin>>n;
    ld pie=6.28318530717958623200;
    pie/=2;
    pie*=2;
    cout<<setprecision(10)<<fixed<<pie<<endl;
    
    
    
    }
    
int main(){
    int t=1;
    // cin>>t;
    while(t--){
        solve();
    }
return 0;
}