#include <fstream>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

int st,dr,n,mid,x,p,sol;

int f(int x)
{
    int z = 5;
    int t = 0;
    while (x/z)
    {
        t += x/z;
        z *= 5;
    }
    return t;
}

int main()
{
    fin >> n;
    st = 1;
    dr = 1000000000;
    sol = -1;
    while (st <= dr)
    {
        mid = (st+dr)/2;
        x = f(mid);
        if (x < n)
            st = mid+1;
        else
            if (x > n)
                dr = mid-1;
            else
            {
                sol = mid;
                dr = mid-1;
            }
    }
    fout << sol;
    return 0;
}