#include <bits/stdc++.h>
std::ifstream fin("fact.in");
std::ofstream fout("fact.out");

int p;

int nrOfZeros(int x)
{
    int p5 = 5, zeros = 0;
    while(p5 <= x)
    {
        zeros += x / p5;
        p5 = p5 * 5;
    }
    return zeros;
}

int binarySearch(int p, int left, int right)
{
   int val = -1;
  while(left <= right)
    {
        int mid = (left + right)/ 2;

        if(nrOfZeros(mid) < p)
                left = mid + 1;
        else
        {
            if(nrOfZeros(mid) == p)
                return val;
            right = mid - 1;
        }
    }

    return -1;
}

int main()
{
    fin >> p;
    fout << binarySearch(p, 1, 1000000001);
    return 0;

}