#include<stdio.h>
long p,nr5,n,x,k,y;
int main()
{
freopen("fact.in","r",stdin);
freopen("fact.out","w",stdout);
scanf("%ld",&p);
n=0;
nr5=0;
y=0;
while(nr5<p)
	{
	n=n+5;
	y++;
	x=y;
	k=1;
	while(x%5==0)
		{
		k++;
		x=x/5;
		}
	nr5=nr5+k;
	}
if(p==0)
	printf("1");
else
	if(nr5==p)
		printf("%ld",n);
	else
		printf("-1");
printf("\n");
return 0;
}