#include <fstream>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

int p;

int zero(int nr)
{
    int zerouri=0;
    while(nr)
    {
        zerouri+=nr/5;
        nr/=5;
    }
    return zerouri;
}

int binara(int p,int lo, int hi)
{
    int mi;
    while (lo <= hi)
    {
        mi=lo+(hi-lo)/2;
        if (zero(mi)>p)
            hi=mi-1;
        else
            if (zero(mi)==p)
                return mi-(mi%5);
            else
                lo=mi+1;
    }
    return -1;
}

int main()
{
    fin >> p;
    fout << binara(p,1,0x3f3f3f3f);
    return 0;
}