#include<stdio.h>
int main()
{
	long k,p,aux;
	int ok;
	FILE *f;
	FILE *g;
	f=fopen("fact.in","r");
	g=fopen("fact.out","w");
	fscanf(f,"%ld",&p);
	k=0;
	ok=1;
	while(p&&ok)
	{
		p--;
		k++;
		aux=k;
		while(aux%5==0)
		{
			p--;
			aux=aux/5;
		}
		if(p<0)
			ok=0;
	}
	if(!ok)
		fprintf(g,"-1");
	else
	{
		if(!k)
			fprintf(g,"1");
		else
			fprintf(g,"%ld",(k*5));
	}
	return 0;
}