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

f.close();
g.close();
return 0;
}