#include <iostream>
#include <fstream>
using namespace std;
  ifstream f("fact.in");
  ofstream g("fact.out");
int nrz(int n)
{
    int ex=0,pp=5;
    while(n>=pp)
    {
        ex+=n/pp;
        pp*=5;
    }
    return ex;
}
int cautbin(int a)
{
    int poz=-1,p=1,u=1000000000;
    while(p<=u)
    {
        int m=p+(u-p)/2;
        int nz=nrz(m);
        if(nz==a)
        {
            poz=m;
            u=m-1;
        }
        else
            if(nz>a)u=m-1;
        else p=m+1;
    }
    return poz;
}
int main()
{
   int p;
   f>>p;
   g<<cautbin(p);
    return 0;
}