#include <iostream>
#include<fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int n,nr,nr5,nr2,x,p;
int main()
{
    f>>p;
    n=2;
    while(p!=nr)
    {
        x=n;
        while(x%2==0)
        {
            nr2++;
            x=x/2;
        }
        while(x%5==0)
        {
            nr5++;
            x=x/5;
        }
        if(nr5!=0&&nr2!=0)
        {
            nr=nr+nr5;
            nr5=0;
            nr2=nr2-nr5;
        }
        n++;
    }
    g<<n-1;

    return 0;
}