#include <iostream>
#include <fstream>


using namespace std;


ifstream fin("fact.in");
ofstream fout("fact.out");

int n;

int nrz(int x)
{
    int s;
    s = 0;
    while(x!=0)
    {
        s += x/5;
        x/=5;
    }
    return s;
}
int bsearch(int st,int dr)
{
    int sol=-1;
    while(st<=dr)
    {
        int mj=(dr+st)/2;
        int x=nrz(mj);
        if(x<n)
        {
            st=mj+1;
        }
        else if(x>n)
        {
            dr=mj-1;
        }
        else
        {
            sol=mj;
            dr=mj-1;
        }
    }
    return sol;
}
int main()
{

    fin>>n;
    fout<<bsearch(1,2000000000);
    return 0;
}