#include <iostream>
#include <fstream>

using namespace std;

ifstream f("fact.in");
ofstream fout("fact.out");
void get_nr_of_5(int x)
{
       int c5=0;
       int i=1,copi;
       while(c5!=x)
        {
        copi=i;
        while(copi%5==0 && copi)
            {
                c5++;
                copi/=5;
            }
        i++;
        }
       fout << i-1;
}
int main()
{

    int x;
    f>>x;
    if(x<0)
        fout << -1;
    else
        if( x == 0)
            fout << 1;
    else
        get_nr_of_5(x);
    return 0;
}