#include <fstream>

using namespace std;
ifstream f("factorial.in");
ofstream g("factorial.out");
long exponent5(int x)
{
    long nr=0,y;
    y=5;
    while(y<=x)
    {
        nr=nr+x/y;
        y=y*5;
    }
    return nr;
}

int main()
{ int n,p,t;
    f>>p;
    n=-1;
    if(p==0)
    n=1;

    else
    {
        for(n=5;(t=exponent5(n))<p;n=n+5)
        if(t>p)
        n=-1;
    }
    g<<n;
}