#include <fstream>
#define NMAX 20000000

using namespace std;
int A[NMAX];
int P;



void proc()
{
	fstream fout("fact.out",ios::out);
	for(int j=1;j<NMAX/5;j*=5)
	for(int i=j;i<NMAX;i+=j)
	{
		A[i]++;
	}
	
	int S=0;
	int i=0;
	while(P>S)
	{
		S=S+A[++i];
	}
	if(P!=0)
		fout<<i*5;
	else fout<<"1";
	fout.close();
}

int main(int argc,char *agv[])
{
	fstream fin("fact.in",ios::in);
	fin>>P;
	
	proc();
	fin.close();
}