#include <iostream>
#include <fstream>
using namespace std;

ifstream f("fact.in");
ofstream g("fact.out");

int pcb(int y)
{
    int x,nr=0;
    x=5;
    while(x<y)
        x=x*5;
    while(x>=5)
    {
        nr=nr+y/x;
        x=x/5;
    }
    return nr;
}
int cb(int l,int r,int nr0)
{
    int mij;
    while(l<=r)
    {
        mij=l+(r-l)/2;
        if(pcb(mij)==nr0)
        {
            if(pcb(mij-1)<nr0||mij==l)
                return mij;
            else
                r=mij-1;
        }
        else
        {
            if(pcb(mij)<=nr0)
                l=mij+1;
            else
                r=mij-1;
        }
    }
    return -1;
}

int p,x;
int main()
{
    f>>p;
    if(p==0)
        g<<"1";
    else
    g<<cb(0,100000000,p);

    return 0;
}