#include<stdio.h>

long v[1000000];
long val(long a)
{
	long s=0;
	while(a>0)
		{
		s+=a/5;
		a/=5;
		}
	return s;
}

long cauta(int a,int b,int n)
{
	long c,t;
	c=(a+b)/2;
	t=val(c);
	if(a==b && t==n ) return b;
	if(a==b) return -1;
	
	
	if(t>=n) return cauta(a,c,n);
	else return cauta(c+1,b,n);

}

int main()
{
	freopen("fact.in","rt",stdin);
	freopen("fact.out","wt",stdout);
	long N;
	scanf("%ld",&N);
	printf("%ld",cauta(1,500000000,N));
	
	
	return 0;
}