using namespace std;
#include <fstream>
ifstream fin("factorial.in");
ofstream fout("factorial.out");


int main()
{
    int i=2, p, n, s=0, p5;
    fin>>p;
    if(p==0) fout<<1;
    else
    {
        while(s<p)
        {
            n=i; p5=0;
            while(n%5==0) {n/=5; p5++;}
            s+=p5;
            i++;
        }
        if(s==p) fout<<i-1;
        else fout<<-1;
    }
    return 0;
}