#include <stdio.h>
long int zero(int n)
{
	long int p=0;
	while(n>=5)
	{
		p+=n/5;
		n/=5;
	}
	return p;
}
int main()
{
	long p,k=0,n=1,u=1;
	FILE *in = fopen("factorial.in","r");
	FILE *out = fopen("factorial.out","w");
	fscanf(in,"%ld",&p);
	//printf("%ld\n",zero(p));
	while(1)
	{
		if(zero(n)==p)
			break;
		n++;
	}
	fprintf(out,"%ld\n",n);
	return 0;
}