#include <fstream>
using namespace std;

int p,nr;
long long n,st,dr,mid;

int zero(long long x)
{
    long long pt=5;
    int sum=0;
    while(pt<=x)
    {
        sum+=x/pt;
        pt=pt*5;
    }
    return sum;
}
int main()
{
    ifstream f("fact.in");
    ofstream g("fact.out");
    f>>p;
    st=1;dr=p*5;
    while(st<=dr)
    {
        mid=(st+dr)/2;
        nr=zero(mid);
        if(nr>=p)
            dr=mid-1;
        else
            st=mid+1;
    }
    if(zero(st)==p)
        g<<st<<"\n";
    else
        g<<"-1"<<"\n";
    f.close();g.close();
    return 0;
}