#include <fstream>

using namespace std;

int zero(int &n)
{
    int x=n, div2=0;
    while(x%2==0)
    {
        x=x/2;
        div2++;
    }
    int y=n, div5=0;
    while(x%5==0)
    {
        y=y/5;
        div5++;
    }
    int r;
    if(div2<=div5) r=div2;
    else r=div5;
    return r;
}

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

    int p;
    f >> p;

    int k=0, n=1;
    while(k<p)
    {
        k=k+zero(n);
        if(k<p) n++;
    }
    if(k==p) g << n;
    else g << -1;
}