#include <iostream>
#include <fstream>

using namespace std;

ifstream f("fact.in");
ofstream g("fact.out");

long long solve(long long val)
{
    int p = 5, cont = 0;
    while(p <= val)
    {
        cont += (val / p);
        p *= 5;
    }
    return cont;
}

int main()
{
    long long p, i = 1;

    f>>p;

    while(solve(i) < p)
    {
        i++;
    }
    g<<i;

    return 0;
}