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 <iostream>
#include <string>
#include <cstdlib>
#include <cmath>
#include <fstream>

using namespace std;

class inPoint{
public:
  int x;
  int y;
};

class Delta{
public:
  inPoint p[3];
};

class Circle{
public:
  inPoint p;
  int radius;
};

double distance(inPoint *p1, inPoint *p2){
  return sqrt((p1->x-p2->x)*(p1->x-p2->x)+(p1->y-p2->y)*(p1->y-p2->y));
}

double dist_line(inPoint *pl1, inPoint *pl2, inPoint *p){
  int a = pl1->x - pl2->x;
  int b = pl2->y - pl1->y;
  int c = pl1->y * pl2->x - pl1->x * pl2->y;
  double ans = b * p->x + a * p->y + c;
  ans = (ans >= 0) ? ans : -ans;
  return ans / sqrt(a*a + b*b);
}
int main(void){
  string str;
  /*
  ifstream ifs("../input.txt");
  if (ifs.fail()) {
      cerr << "cannot find the file" << endl;
      return 1;
  }
  */
  while(1){
    Circle *c = (Circle *) malloc(sizeof(Circle));
    Delta *d = (Delta *) malloc(sizeof(Delta));
    for (int i = 0; i < 5; i++) {
      getline(cin, str);

      if(i == 0 && str == "0 0") break;

      int j;
      for(j = 0; j <(int) str.size(); j++){
          if(str[j] == ' '){
            str[j] = '\0';
            break;
        }
      }
      switch(i){
        case 0:
        case 1:
        case 2:
        d->p[i].x = atoi(str.c_str());
        d->p[i].y = atoi(&str[j+1]);
        break;
        case 3:
        c->p.x = atoi(str.c_str());
        c->p.y = atoi(&str[j+1]);
        break;
        case 4:
        c->radius = atoi(str.c_str());
        break;
      }

    }
    if(str == "0 0") break;


    if(distance(&d->p[0], &c->p) < c->radius&& distance(&d->p[1], &c->p) < c->radius&& distance(&d->p[2], &c->p) < c->radius){
      cout << 'b' << endl;
    }
    else if(dist_line(&d->p[0], &d->p[1], &c->p) > c->radius&& dist_line(&d->p[0], &d->p[2], &c->p) > c->radius&& dist_line(&d->p[1], &d->p[2], &c->p) > c->radius){
        if (dist_line(&d->p[0], &d->p[1], &d->p[2]) < distance(&d->p[0], &c->p) && dist_line(&d->p[1], &d->p[2], &d->p[0]) < distance(&d->p[1], &c->p) && dist_line(&d->p[2], &d->p[0], &d->p[1]) < distance(&d->p[2], &c->p))
            cout << 'd' << endl;
        else
            cout << 'a' << endl;
    }
    else{
      cout << 'c' << endl;
    }
  }
  return 0;
}

C++: #include <iostream>
#include <string>
#include <cstdlib>
#include <cmath>
#include <fstream>

using namespace std;

struct Point{
  int x;
  int y;
};

struct Delta{
  Point p[3];
};

struct Circle{
  Point p;
  int radius;
};

double distance(Point p1, Point p2){
  return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));
}

double dist_line(Point pl1, Point pl2, Point p){
  int a = pl1.x - pl2.x;
  int b = pl2.y - pl1.y;
  int c = pl1.y * pl2.x - pl1.x * pl2.y;
  double ans = b * p.x + a * p.y + c;
  ans = (ans >= 0) ? ans : -ans;
  return ans / sqrt(a*a + b*b);
}
int main(void){
  string str;
  /*
  ifstream ifs("../input.txt");
  if (ifs.fail()) {
	  cerr << "cannot find the file" << endl;
	  return 1;
  }
  */
  while(1){
    Circle *c = (Circle *) malloc(sizeof(Circle));
	Delta *d = (Delta *) malloc(sizeof(Delta));
	for (int i = 0; i < 5; i++) {
//		getline(ifs, str);
		cin >> str;

      if(str == "0 0") break;
	  
      int j;
      for(j = 0; j <(int) str.size(); j++){
	      if(str[j] == ' '){			
			str[j] = '\0';
			break;
        }
      }
      switch(i){
        case 0:
        case 1:
        case 2:
        d->p[i].x = atoi(str.c_str());
        d->p[i].y = atoi(&str[j+1]);
        break;
        case 3:
        c->p.x = atoi(str.c_str());
        c->p.y = atoi(&str[j+1]);
        break;
        case 4:
        c->radius = atoi(str.c_str());
        break;
      }
	  
    }
    if(str == "0 0") break;
	

    if(distance(d->p[0], c->p) <= c->radius&& distance(d->p[1], c->p) <= c->radius&& distance(d->p[2], c->p) <= c->radius){
      cout << 'b' << endl;
    }
    else if(dist_line(d->p[0], d->p[1], c->p) >= c->radius&& dist_line(d->p[0], d->p[2], c->p) >= c->radius&& dist_line(d->p[1], d->p[2], c->p) >= c->radius){
		if (dist_line(d->p[0], d->p[1], d->p[2]) <= distance(d->p[0], c->p) && dist_line(d->p[1], d->p[2], d->p[0]) <= distance(d->p[1], c->p) && dist_line(d->p[2], d->p[0], d->p[1]) <= distance(d->p[2], c->p))
			cout << 'd' << endl;
		else
			cout << 'a' << endl;
    }
    else if(dist_line(d->p[0], d->p[1], c->p) <= c->radius|| dist_line(d->p[0], d->p[2], c->p) <= c->radius|| dist_line(d->p[1], d->p[2], c->p) <= c->radius){
      cout << 'c' << endl;
    }
    else{

    }
	
  }
  return 0;
}