#include <bits/stdc++.h>

using namespace std;

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

int cer,st,dr,mj,zeros,a;

int main()
{
    f >> cer;
    if(!cer)
    {
        g << 1;
        return 0;
    }
    st = 1;
    dr = 10 * cer;
    while(st <= dr)
    {
        mj = st + (dr - st) / 2;
        zeros = 0;
        a = mj;
        while(a)
        {
            zeros += a / 5;
            a /= 5;
        }
        if(cer < zeros)
            dr = mj - 1;
       else if(cer > zeros)
            st = mj + 1;
        else
        {
            g << mj / 5 * 5;
            return 0;
        }
    }
    g << -1;
    return 0;
}