#include <iostream>
#include <fstream>
using namespace std;
int p,x;
ifstream f("fact.in");
ofstream g("fact.out");
int desc(int k)
{int l=0;
    if(k%5==0)
      {while(k%5==0)
    {
        l++;k=k/5;
    }return l;}return 0;
}
int num()
{int i=0;x=0;
    while(x<=p)
    {  i++;
       x=x+desc(i);
         if(x==p)
            return i;

    } return -1;
}
int main()
{
    f>>p;
    g<<num();
    return 0;
}