#include<iostream>
#include<fstream>
using namespace std;
unsigned n;
unsigned fact(unsigned x)
{
    unsigned s=1;
    for(unsigned i=1;i<=x;i++)
        s=s*i;
    return s;
}
int main()
{
    ifstream f("fact.in");
    f>>n;
    f.close();
    int i=1,k=0,aux;
    while(k!=n)
    {
        k=0;
        aux=fact(i);

        while(aux%10==0)
        {
            k++;
            aux=aux/10;
        }
       i++;
    }
    ofstream g("fact.out");
    g<<i-1;
}