#include<fstream>

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

int contor5(int n)
{
    int c=0, i;

    for(i=5;i<=n;i*=5)
        c+=n/i;

    return c;

}

int main()
{

    int p,st=1,dr=100000000,m,c5;

    f>>p;

    while(st<dr)
    {
        m=(st+dr)/2;
        c5=contor5(m);

        if(c5<p)
            st=m+1;
        else
            dr=m-1;
    }

    c5=contor5(m);
    if(c5==p)
        g<<st;
    else
        g<<-1;

    return 0;
}