# include <stdio.h>
int f(int n){
	int c=0;	
	while(n){
		c+=n/5;
		n/=5;
	}
	return c;
}

int main (){
	freopen("factorial.in","r",stdin);
	freopen("factorial.out","w",stdout);
	int p;
	long s,d,m;
	scanf("%d",&p);
	s=1;
	d=800000000;
	while(s!=d){
		m=(s+d)/2;
		if(f(m)<p)
			s=m+1;
		else
			d=m;
	}
	if(p==f(s))
		printf("%ld",s);
	else
		printf("-1");
	return 0;
}