#include <fstream>

using namespace std;
int p;

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

int NRZ(int x)
{
    int s;
    s = 0;
    while(x!=0)
    {
        s += x/5;
        x/=5;
    }
    return s;
}

int main()
{
    int i,st,dr,s,m,t;
    fin>>p;
    t = -1;
    st = 1;
    dr = 2000000000;
    while(st<=dr)
    {
        m = (st+dr)/2;
        s = NRZ(m);
        if(s<p) st = m+1;
        else if(s>p) dr = m-1;
        else
            {
            t = m;
            dr = m-1;
            }
    }
    fout<<t<<"\n";



    fout.close();
    return 0;
}