#include<iostream.h>
#include<fstream.h>
ifstream f("fact.in");
ofstream g("fact.out");
long num,p,i,t,k=0;
int factorial (int num)
{
 if (num==1)
  return 1;
 return factorial(num-1)*num;
}
int main()
{
    long n=50;
    f>>p;
    if(i==1) g<<1;
    for(i=2;i<=n;i++)
    {
    t=factorial(i);
    while(t>0)
    {k++;
    t=t/10;}
    if(k==p)
    {g<<i;
    break;}
    if(i==n)
    g<<(-1);
    k=0;
}

f.close();

return 0;
}