#include <iostream>
#include<fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int expp(int n, int p)
{
    int s = 0, pp = p;
    while(n >= pp)
    {
        s += n / pp;
        pp *= p;
    }
    return s;
}
int cautbin(int X)
{
    int p = 1, u = 0x7fffffff, N = -1;
    while(p <= u)
    {
        int m = p + (u - p) / 2;
        int zm = expp(m, 5);
        if(X == zm)
            N = m;
        if(X <= zm)
            u = m - 1;
        else
            p = m + 1;
    }
    return N;
}
int main()
{
    int P;
    f >> P;
    g << cautbin(P);
    return 0;
}