#include <fstream>
#include <math.h>

using namespace std;

long long zero (int x)
{
    int nr=0,p=5;
    while (x>=p)
    {
        nr+=x/p;
        p*=5;
    }
    return nr;
}

int cautare(int dr, int p)
{
    int st=1,nr=-1,mid;
    while (st<=dr)
    {
        mid=(st+dr)/2;
        if (zero(mid)==p)
            nr=mid;
        if (zero(mid)>=p)
            dr=mid-1;
        else
            st=mid+1;
    }
    return nr;
}




int main()
{
    ifstream f("fact.in");
    ofstream g("fact.out");
    long long p,i,j,nr=0,tmp;
    f>>p;
    if (p==0)
        g<<1;
    else
    {
        g<<cautare(5*p,p);
    }
    return 0;
}