#include <fstream>
#include <climits>
using namespace std;
ifstream fin ("fact.in");
ofstream fout ("fact.out");
long long st=1, dr=100000000, mij, val, k=-1, p;

long long zero(long long n)
{
    long long nr=0, x=5;
    while(x<=n)
    {
        nr+=n/x;
        x*=5;
    }
    return nr;
}
int main()
{
    fin>>p;
    if(p==0)
    {
        fout<<"1\n";
        return 0;
    }
    while(st<=dr)
    {
        mij=(st+dr)/2;
        val=zero(mij);
        if(val==p)
        {
            k=mij;
            dr=mij-1;
        }
        else if (val>p)dr=mij-1;
        else st=mij+1;
    }
    fout<<k<<"\n";



    return 0;
}