Go: package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
	"strings"
)

var scanner = bufio.NewScanner(os.Stdin)

func main() {
	for scanner.Scan() {
		buf0 := strings.Split(scanner.Text(), " ")
		input0 := make([]int, 2)
		for i := range input0 {
			input0[i], _ = strconv.Atoi(buf0[i])
		}
		if input0[0] == 0 && input0[1] == 0 {
			break
		}
		a, b := input0[0], input0[1]
		scanner.Scan()
		buf1 := strings.Split(scanner.Text(), " ")
		input1 := make([]int, 2)
		for i := range input1 {
			input1[i], _ = strconv.Atoi(buf1[i])
		}
		c, d := input1[0], input1[1]
		scanner.Scan()
		buf2 := strings.Split(scanner.Text(), " ")
		input2 := make([]int, 2)
		for i := range input2 {
			input2[i], _ = strconv.Atoi(buf2[i])
		}
		e, f := input2[0], input2[1]
		scanner.Scan()
		buf3 := strings.Split(scanner.Text(), " ")
		input3 := make([]int, 2)
		for i := range input3 {
			input3[i], _ = strconv.Atoi(buf3[i])
		}
		g, h := input3[0], input3[1]
		scanner.Scan()
		r, _ := strconv.Atoi(scanner.Text())
		if (a-g)*(a-g)+(b-h)*(b-h) <= r*r && (c-g)*(c-g)+(d-h)*(d-h) <= r*r && (e-g)*(e-g)+(f-h)*(f-h) <= r*r {
			fmt.Println("b")
		} else if dist(a, b, c, d, g, h) > float64(r)-0.000001 && dist(a, b, e, f, g, h) > float64(r)-0.000001 && dist(e, f, c, d, g, h) > float64(r)-0.000001 && inclusive(a, b, c, d, e, f, g, h) {
			fmt.Println("a")
		} else if CL_intersect(a, b, c, d, g, h, r) || CL_intersect(a, b, e, f, g, h, r) || CL_intersect(e, f, c, d, g, h, r) {
			fmt.Println("c")
		} else {
			fmt.Println("d")
		}
	}
}

func CL_intersect(ax, ay, bx, by, cx, cy, r int) bool {
	acx := cx - ax
	acy := cy - ay
	bcx := cx - bx
	bcy := cy - by
	abx := bx - ax
	aby := by - ay
	if acx*acx+acy*acy >= r*r || bcx*bcx+bcy*bcy >= r*r {
		if abx*acx+aby*acy < 0 {
			if acx*acx+acy*acy <= r*r {
				return true
			}
		} else {
			if abx*acx+aby*acy > abx*abx+aby*aby {
				if bcx*bcx+bcy*bcy <= r*r {
					return true
				}
			} else if acx*acx+acy*acy-(abx*acx+aby*acy)*(abx*acx+aby*acy)/(abx*abx+aby*aby) <= r*r {
				return true
			}
		}
	}
	return false
}

func inclusive(ax, ay, bx, by, cx, cy, px, py int) bool {
	ok1 := true
	ok2 := true
	if (bx-ax)*(py-ay)-(px-ax)*(by-ay) < 0 {
		ok1 = false
	}
	if (bx-ax)*(py-ay)-(px-ax)*(by-ay) > 0 {
		ok2 = false
	}
	if (cx-bx)*(py-by)-(px-bx)*(cy-by) < 0 {
		ok1 = false
	}
	if (cx-bx)*(py-by)-(px-bx)*(cy-by) > 0 {
		ok2 = false
	}
	if (ax-cx)*(py-cy)-(px-cx)*(ay-cy) < 0 {
		ok1 = false
	}
	if (ax-cx)*(py-cy)-(px-cx)*(ay-cy) > 0 {
		ok2 = false
	}
	return ok1 || ok2
}

func dist(ax, ay, bx, by, px, py int) float64 {
	dx := float64(bx - ax)
	dy := float64(by - ay)
	A := float64(dx*dx + dy*dy)
	B := dx*float64(ax-px) + dy*float64(ay-py)
	t := -B / A
	if t < 0 {
		t = 0
	}
	if t > 1 {
		t = 1
	}
	tx := float64(ax) + dx*t
	ty := float64(ay) + dy*t
	return math.Sqrt((float64(px)-tx)*(float64(px)-tx) + (float64(py)-ty)*(float64(py)-ty))
}

C++: #include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <ctime>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <cstring>
#include <vector>
#include <algorithm>
#include <functional>
#include <fstream>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <cstring>
#include <numeric>
#include <cassert>
using namespace std;
static const double EPS = 1e-10;
typedef long long ll;
#define rep(i,n) for(int i=0;i<n;i++)
#define rev(i,n) for(int i=n-1;i>=0;i--)
#define all(a) a.begin(),a.end()
#define mp(a,b) make_pair(a,b)
#define pb(a) push_back(a)
#define SS stringstream
#define DBG1(a) rep(_X,sz(a)){printf("%d ",a[_X]);}puts("");
#define DBG2(a) rep(_X,sz(a)){rep(_Y,sz(a[_X]))printf("%d ",a[_X][_Y]);puts("");}
#define bitcount(b) __builtin_popcount(b)
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)

typedef complex<double> P;

int chk(P a,P b,double r){
	double t = abs(a-b) - r;
	if( fabs(t) < EPS ) return 0;
	return t < 0 ? -1 : 1;
}
double cross(P a,P b){
	return imag(a*conj(b));
}


int main(){
	P a,b,c,d;
	double r;
	while(cin >> a.real() >> a.imag() , a.real() != 0 || a.imag() != 0 ){
		cin >> b.real() >> b.imag();
		cin >> c.real() >> c.imag();
		cin >> d.real() >> d.imag();
		cin >> r;
		
		int in = 0;
		int mk = cross(a-d,b-d) <= 0 ;
		if( mk == (cross(b-d,c-d) <= 0) && mk == (cross(c-d,a-d) <= 0)){
			in = 1;
		}
		
		if( chk(a,d,r) <= 0 &&  chk(b,d,r) <= 0 &&  chk(c,d,r) <= 0 ){
			cout << "b" << endl;
		}else if( chk(a,d,r) >= 0 &&  chk(b,d,r) >= 0 &&  chk(c,d,r) >= 0){
			if( in ){
				cout << "a" << endl;
			}else{
				cout << "d" << endl;
			}
		}else{
			cout << "c" << endl;
		}
	

		
	}
}

C++: #include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <cmath>
#include <stack>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <list>
#include <iostream>
#include <sstream>
#include <climits>
#include <cfloat>
#include <complex>


typedef long long ll;
const double Eps = 1e-6;

using namespace std;

typedef complex<double> Point;

double dot(const Point& a, const Point& b)
{
	return a.real()*b.real() + a.imag()*b.imag();
}
double cross(const Point& a, const Point& b)
{
	return a.real()*b.imag() - a.imag()*b.real();
}
double distance_line_point(const Point& point, const Point& a, const Point& b)
{
	return abs(cross(a-b, point-b) / abs(a-b));
}
double distance_linesegment_point(const Point& point, const Point& a, const Point& b)
{
	if (dot(b-a, point-a) < Eps)
		return abs(a-point);
	else if (dot(a-b, point-b) <Eps)
		return abs(b-point);
	else
		return distance_line_point(a, b, point);
}
bool is_in_triangle(const Point& point, const Point* triangle)
{
	double t[3];
	for (int i = 0; i < 3; ++i)
		t[i] = cross(triangle[(i+1)%3] - triangle[i], point - triangle[i]);

	return t[0] >= 0 && t[1] >= 0 && t[2] >= 0
		|| t[0] <= 0 && t[1] <= 0 && t[2] <= 0;
}
bool is_in_triangle(const Point& point, const Point& a, const Point& b, const Point& c)
{
	Point t[3] = { a, b, c };
	return is_in_triangle(point, t);
}
bool is_circle_in_triangle(const Point& center, double radius, const Point* triangle)
{
	if (!is_in_triangle(center, triangle))
		return false;
	for (int i = 0; i < 3; ++i)
		if (distance_line_point(triangle[i], triangle[(i+1)%3], center) < radius)
			return false;
	return true;
}
bool is_triangle_in_circle(const Point* triangle, const Point& center, double radius)
{
	for (int i = 0; i < 3; ++i)
		if (abs(triangle[i]-center) > radius)
			return false;
	return true;
}
bool interect_triangle_circle(const Point* triangle, const Point& center, double radius)
{
	for (int i = 0; i < 3; ++i)
		if (distance_linesegment_point(center, triangle[i], triangle[(i+1)%3]) < radius - Eps)
			return true;
	return false;
}

int main()
{
	int x[4], y[4], r;
	while (true)
	{
		for (int i = 0; i < 4; ++i)
			scanf("%d %d", x+i, y+i);
		scanf("%d", &r);
		if (x[0] == 0 && y[0] == 0)
			break;
		Point p[4];
		for (int i = 0; i < 4; ++i)
			p[i] = Point(x[i], y[i]);

		if (is_circle_in_triangle(p[3], r, p))
			puts("a");
		else if (is_triangle_in_circle(p, p[3], r))
			puts("b");
		else if (interect_triangle_circle(p, p[3], r))
			puts("c");
		else
			puts("d");
	}

	return 0;
}