#include<fstream>

using namespace std;

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

long long n,i,nr,s,j;
int main()
{
    f>>n;
    while(s<n)
    {
        i++;
        j=i;
        nr=1;
        while(j%5==0)
        {
            j/=5;
            nr++;
        }
        s+=nr;
    }
    if(s==0)
        g<<1;
    else
    if(s==n)
        g<<i*5;
    else
        g<<-1;
}