#include <fstream>
#include <iostream>

using namespace std;
int main ( )
{
    int P;
    ifstream fin ("fact.in");
    fin >> P;
    long long int x = 1;
    int nrz = 0;
    int N;
    if ( P == 0 )
        N = 1;
    else
        for ( int i = 1 ; i < 100000000 ; ++ i )
        {
            x = x * i;
            if ( x % 10 == 0 )
            {
                ++ nrz;
                x /= 10;
            }
            if ( nrz == P )
            {
                N = i;
                break;
            }
        }
    ofstream fout ("fact.out");
    fout << N;
    fin.close ();
    fout.close ();
    return 0;
}