#include <fstream>
#include <iostream>

using namespace std;

int main()
{
int d=0,c=0,z=0,min;
long p,aux,i;
ifstream f;
ofstream g;

    f.open("fact.in");
    f>>p;
    f.close();

    g.open("fact.out");
    if (p==0) g<<1;
    else if (p<0) g<<-1;
    else {
    for (i=1;z<p;i++) {if (i%2==0) {aux=i; while (aux%2==0) {d++; aux/=2;}}
                       if (i%5==0) {aux=i; while (aux%5==0) {c++; aux/=5;}}
                       if (d==0||c==0) min=0;
                       else if (d<=c) min=d;
                       else if (c<d) min=c;
                       z+=min;
                       d-=min;
                       c-=min;
                      }

    g<<i-i%5;
    }

    g.close();

return 0;
}