#ifdef __unix__
#include <bits/stdc++.h>
#else
#include <iostream>
#include <algorithm>
#include <math.h>
#include <functional>
#include <vector>
#include <string>
#include <map>
#include <set>
#include <unordered_set>
#include <stack>
#include <bitset>
#endif

#define fastIO ios_base::sync_with_stdio(0), cin.tie(NULL)
#define pb push_back
#define all(x) x.begin(), x.end()
#define endl '\n'
#define mkp make_pair
/*#define NUMTOSTR(x)  (unsigned char)((x) + 48);*/
typedef unsigned int uint;
typedef long long ll;
typedef unsigned long long  ull;
using namespace std;

int main(){
	fastIO;
	string s;
	cin >> s;
	if (s.size() == 2) cout << s;
	else {
		reverse(all(s));
		cout << s;
	}
	return 0;
}

#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <cmath>
#include <queue>
#include <set>
#include <map>
#include <iomanip>
#include <fstream>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
const int mod = 1000000007;

int main() {
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    cout << n * 3.141592653589 * 2;
}
