#include <fstream>
#include <math.h>
#include <limits.h>

using namespace std;

long long int zeros(long long int x)
{
    long long int zeros = 0, k;
    for(k = 0; pow(5,k) <= x; k++);
    for(int i = 1; i <= k - 1; i++)
        zeros += (x / pow(5,i));
    return zeros;
}

long long int search(long long int p)
{
    if(p == 0)
        return 1;
    long long int first = 1, last = LLONG_MAX;
    while(first <= last)
    {
        long long int mid = (first + last) / 2;
        if(zeros(mid) == p)
        {
            while(zeros(mid) == p)
                mid--;
            return mid + 1;
        }
        else
        {
            if(p > zeros(mid))
                first = mid + 1;
            else
                last = mid - 1;
        }
    }
    return -1;
}
int main()
{
    ifstream in("fact.in");
    long long int p;
    in >> p;
    in.close();
    ofstream out("fact.out");
    out << search(p);
    out.close();
}