#include <fstream>
#include <vector>

using namespace std;

ifstream in ("fact.in");
ofstream out ("fact.out");

long long legendre(long long x)
{
    long long t=5,p=0;
    while (t<=x)
        p+=x/t,t*=5;
    return p;
}

long long cautbin(long long val)
{
    long long mijl,st=1,dr=1000000000,x=-1;
    while (st<=dr)
    {
        mijl=(st+dr)/2;
        long long t=legendre(mijl);
        if (t==val)
            x=mijl,dr=mijl-1;
        else if (t<val)
            st=mijl+1;
        else 
            dr=mijl-1;
    }
    return x;

}

int main()
{
    long long n;
    in>>n;
    out<<cautbin(n);
    return 0;
}