#include<stdio.h>
#include<math.h>
long int nr_zerouri(long int x)
{
	int k=0;
	long int suma=0,putere;
	do
	{
		k++;
		putere=(int)pow(5*1.0,k*1.0);
		suma+=x/putere;
	}while(x/putere);
	return suma;
}
int main()
{
	long int i,cerinta,P;
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	scanf("%d",&P);
	if(P==0)
		printf("1");
	else
	{
	cerinta=P;
	P=4*P;
	for(i=P;i;i++)
		if(nr_zerouri(i)==cerinta)
		{printf("%d",i);break;}
	}
	return 0;
}