static private double C(int a,int b) {
		if(b<=0) {
			System.out.println("Error: b should be positive.");
			return -1;
		}
		
		if(a == 0 || a == b)
			return 1;
		
		if(a>b)
			return 0;
		double c = 1;
		for(int i=b-a+1;i<=b;i++) {
			if(c > Double.MAX_VALUE) {
				c = Double.MAX_VALUE;
				break;
			}
			c*=i;
		}
		
		return c;
	}