#include<stdio.h>
FILE *in,*out;
int nr5,p;
int num,aux;
int main()
{
	in=fopen("factorial.in","rt");
	out=fopen("factorial.out","wt");
	fscanf(in,"%d",&p);
	if(p>0)
	{
		for(;;)
		{
			if(nr5>=p)
				break;
			num++;
			aux=num;
			while(aux%5==0)
			{
				nr5++;
				aux/=5;
			}
		}
		fprintf(out,"%d",num);
	}
	else
		fprintf(out,"1");
		
	return 0;
}