#include <fstream>
#include <string>
#include <sstream>

using namespace std;

int main()
{
    ifstream in("INPUT.txt");
    ofstream out("OUTPUT.txt");
    unsigned a;
    string sum("7182818284590452353602875");
    in >> a;
    if(a == 0)
        out << 3;
    else
    {
        int temp, temp2;
        string str = sum.substr(a,1);
        string str2 = sum.substr(a-1,1);
        stringstream stream(str);
        stream >> temp >> str;
        stringstream stream2(str2);
        stream2 >> temp2 >> str2;
        if(temp >= 5 && a!=sum.size())
        {
            temp2++;
            ostringstream stream3;
            stream3 << temp2;
            str = stream3.str();
            sum.replace(a-1,1,str);
        }
        sum.erase(a,sum.size());
        out << "2." << sum;

    }
    return 0;
}