#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <climits>

using namespace std;

FILE * f = fopen("factorial.in", "r");
FILE * g = fopen("factorial.out", "w");

int zerouri(int x)
{
    int p = 25, z = 5, nr = 0;
    nr = x / z;
    while (p <= x)
    {
        nr += x / p;
        p *= z;
    }
    return nr;
}

int cautare(int n)
{
    int l = 1 << 29, s = 0;
    while (l != 0)
    {
        if (zerouri(s + l) < n)
            s += l;
        l >>= 1;
    }
    if (zerouri(s + 1) == n)
        return s + 1;
    return -1;
}

int main()
{
    int n;
    fscanf(f, "%i", &n);
    fprintf(g, "%i", cautare(n));
    return 0;
}