#include<iostream>
#include<fstream>
using namespace std;
int main()
{long p,i=0,nr=0,nr2=0,nr5=0,cop;
ifstream f("fact.in");
ofstream g("fact.out");
f>>p;
if(p==0)
	g<<1;
else
	while(nr<p)
	{i=i+1;cop=i;
	while(cop%2==0)
		{nr2=nr2+1;cop=cop/2;}
	while(cop%5==0)
		{nr5=nr5+1;cop=cop/5;}
	if(nr2>0&&nr5>0)
	  if(nr2>nr5)
	  {nr2=nr2-nr5;nr=nr+nr5;
	  nr5=0;
	  }
	  else
	  {nr5=nr5-nr2;nr=nr+nr2;
	  nr2=0;
	  }
	}
	g<<i;
	f.close();
	g.close();
	return 0;
}