#include <fstream>
#include <iostream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int main()
{
int s=0,n=0,p,r=1,k=0,i=0;
in>>p;
if (p==0)
    n=1;
else
    while (s<p) {
        i++;
        if (i%5==0){
            k++;
            if (k%5==0)
                r++;
            s=s+r;
        }
        n=n+5;
        s=s+1;
    }
if (s>p)
    n=-1;
out<<n;
    return 0;
}