using namespace std;
#include<cstdio>
#define NMax 2000005
int v[NMax];
int main()
{
	long long p,r,c,i;
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	scanf("%d",&p);
	for(i=1;v[i-1]<p;i++)
	{
		r=i; c=1;
		while(r%5==0)
		{
			c++;
			r=r/5;
		}
		v[i]=v[i-1]+c;
	}
	i--;
	if(v[i]==p)
		printf("%d",5*i);
	else
		printf("-1");
	return 0;
}