//Problema factorial - Infoarena

#include<stdio.h>

int p;
long x,y,m;

long nrz(long);

int main()
{
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);

	scanf("%d",&p);

	if(p==0)
		printf("1");
	else
	{
		x=0;
		y=2000000000;

		while(x<y)
		{
			m=(x+y)/2;

			if(p==nrz(m))
			{
				x=m;
				y=m;
			}
			else
			{
				if(p>nrz(m))
					x=m+1;
				else
					y=m-1;
			}
		}

		if(nrz(x)!=p&&nrz(x+1)!=p)
			printf("-1");
		else
		{
			if(nrz(x)==p)
			{
				x=x-(x%5);
				printf("%ld",x);
			}
			else
				printf("%ld",x+1);
		}
	}

	return 0;
}
long nrz(long z)
{
	long a;
	long b;
	a=5;
	b=0;

	while(z>=a)
	{
		b=b+z/a;
		a*=5;
	}

	return b;
}