#include <fstream>

using namespace std;

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

int f(int x)
{
    int k=0;
    while(x!=0)
    {
        k+=x/5;
        x/=5;
    }
    return k;
}

int main()
{
    int n,p,l,r,mij,sol=1;
    fin>>p;
    l=1;
    r=5*p;
    while(l<=r)
    {
        mij=(l+r)/2;
        if(f(mij)>=p)
        {
            r=mij-1;
            sol=mij;
        }
        else
        {
            l=mij+1;
        }
    }
    if(f(sol)==p)
        fout<<sol<<"\n";
    else
        fout<<"-1\n";
    return 0;
}