#include<iostream>
#include<math.h>
#include<fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int n;
long long p;
int numara_zero(int x)
{
    int i, s=0, r=5;
    while(x/r!=0)
    {
        s+=x/r;
        r*=5;
    }
    return s;
}
int cautare_binara(int st, int dr)
{
    int mijloc, t;
    mijloc=(st+dr)/2;
    t=numara_zero(mijloc);
    if(st!=dr)
    {
        if(t<p)
            return cautare_binara(mijloc+1, dr);
        else return cautare_binara(st, mijloc);
    }
    else
        if(t==p)
            return mijloc;
        else return -1;
}
int main()
{
    f>>p;
    g<<cautare_binara(1, 1<<30);
}