#include <iostream>
#include <fstream>
using namespace std;
int P;
int suma(int nr)
{
	int s=0,x=nr,a=5;
	while (x!=0)
	{
		s+=nr/a;
		a*=5;
		x=x/5;
	}
	return s;

}


int main()
{
ifstream fin("fact.in");
ofstream fout("fact.out");
int M,st=1,dr;
fin>>P;
//n=4*P;
dr=10000000;
//M=st+(dr-st)/2;
//fout<<st<<" "<<dr<< " " <<P;



if(P==0)
	fout<<1;

else
{
	while (st < dr)
	{
		M=(st+dr)/2;
	if(suma(M)>P)
		dr=M-1;
	else
		//if(suma(M)<P)
			st=M+1;
	
	
	
	}
while(suma(M)>=P)
{
	M--;
}
fout<<M+1;
}

//fout<<suma(10);
	return 0;
}