#include<cstdio>
#define filein "fact.in"
#define fileout "fact.out"
using namespace std;

int main()
{
	freopen (filein,"r",stdin);
	freopen (fileout,"w",stdout);
	unsigned int n,p,s,k;
	bool ok=true;
	scanf("%d",&p);
	if (p==0) {printf("1"); return 0;}
	n=-1;
	while (ok)
	{
		n++;
		k=5;
		s=0;
		while (n/k>0)
		{
			s=s+n/k;
			k=k*5;
		}
		if (s==p) ok=false;
		if (s>p) 
		{
			printf("-1");
			return 0;
		}
	}
	printf("%d",n);
	return 0;
}