#include <fstream>
using namespace std;
int main()
{
	ifstream fi("fact.in");
	ofstream fo("fact.out");
	long n,nfact;
	n=1;
	int t,i,p,m,k;
	fi >> p;
	t=0;
	while (t==1)
	{ nfact = 1;
          for (i=1;i<=n;i++)
          nfact = (nfact * i);
          while (nfact !=0)
          {
          m = (nfact%10);
          nfact = (nfact/10);
          if (m == 0)
          k++;
          }
    if (k == p)
    {
    fo << n; 
    t=1;
}  
else
    n++;     
}      
}