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++: 
    B comp(const P& l, const P& r){ return (l.X == r.X) ? l.Y < r.Y : l.X < r.X; }
    typedef pair<P, P> L;  //line
    typedef pair<P, P> LS; //line segment
    typedef pair<P, D> C;  //circle
    typedef vector<P> Poly;
    const D EPS = 1e-8;
    //Decompotision Macro
#define DCl(a,b,l) P (a),(b);tie(a,b)=l; 
#define DCc(a,b,c) P (a);D (b);tie(a,b)=c; 
    
    //A dot B
    IL D dot(P a, P b) { return a.X*b.X + a.Y*b.Y; }
    //A cross B
    IL D cross(P a, P b) { return a.X*b.Y - a.Y*b.X; }
    IL D ccw(P a,P b,P c){
        return cross(b - a, c - a);
    }

    IL int sgn(P a,P b, P c){
        if(cross(b-a,c-a) > EPS)return 1;
        if(cross(b-a,c-a) < -EPS)return -1;
        if(dot(b-a,c-a) < -EPS)return 2; // b-a-c
        if(dot(a-b,c-b) < -EPS)return -2; // a-b-c
        return 0;
    }
    IL D signed_distance_P_L(P p, L l) {
        DCl(a,b,l);
        return ccw(a,b,p)/ abs(b - a);
    }
    
    IL D distance_P_L(P p, L l) {
        return abs(signed_distance_P_L(p,l));
    }

    IL D distance_P_LS(P p, LS ls) {
        DCl(a,b,ls);
        if (dot(b - a, p - a) < EPS) return abs(p - a);
        if (dot(a - b, p - b) < EPS) return abs(p - b);
        return abs(cross(b - a, p - a)) / abs(b - a);
    }

    
    IL B is_L_L(L p, L q) {
        DCl(a,b,p);
        DCl(c,d,q);
        return
            abs(cross(a - b, c - d)) > EPS ||
            abs(cross(a - b ,d - b)) < EPS;
    }
    IL B is_L_LS(L l, LS ls) {
        DCl(a,b,l);
        DCl(c,d,ls);
        return ccw(a,b,c)*ccw(a,b,d)<EPS;
    }
    IL B is_LS_LS(LS p, LS q) {
        DCl(a,b,p);
        DCl(c,d,q);
        return sgn(a,b,c)*sgn(a,b,d) <= 0
            && sgn(c,d,a)*sgn(c,d,b) <= 0;
    }

    IL D distance_LS_LS(LS p,LS q){
        if(is_LS_LS(p,q))return 0;
        return min({
                distance_P_LS(p.fi,q),
                distance_P_LS(p.se,q),
                distance_P_LS(q.fi,p),
                distance_P_LS(q.se,p)    
                    });
    }

    //caution: have to use isintersected_L_L before this function
    IL P cross_point_L_L(L p, L q) {
        DCl(a,b,p);
        D d1 = signed_distance_P_L(a, q);
        D d2 = signed_distance_P_L(b, q);
        return (a * d2 - b * d1) / (d2 - d1);
    }
    
    IL B is_C_C(C p, C q) {
        DCc(cp,rp,p);
        DCc(cq,rq,q);
        D d = abs(cp - cq);
        return abs(rp - rq) - d <EPS &&
                                 rp + rq - d > -EPS;
    }
    IL LS cross_C_C(C p, C q) {
        DCc(cp,rp,p);
        DCc(cq,rq,q);
        D d = abs(cp - cq);
        D rc = (d*d + rp*rp - rq*rq) / (2 * d);
        D rs = sqrt(rp*rp - rc*rc);
        P diff = (cq - cp) / d;
        return {cp + P(rc, rs)*diff, cp + P(rc, -rs)*diff};
    }
    IL Poly convex_hull(Poly p) {
        int n = p.size();
        Poly res(2 * n);
        int k = 0, t;
        sort(ALL(p),comp);
        REP(i,n) {
            while (k > 1 && ccw(res[k-2],res[k-1],p[i]) < EPS)k--;
            res[k++] = p[i];
        }
        t = k;
        REP(j,n-1){
            int i= n - 2 - j;
            while (k > t && ccw(res[k - 2],res[k - 1], p[i]) < EPS)k--;
            res[k++] = p[i];
        }
        res.resize(k - 1);
        return res;
    }
    IL B convex_in(Poly& l,P& p) {
        int a = 0, b = l.size(), c;
        D A, C;
        P g = (l[a] + l[b - 1] + l[b / 2]) / 3.0;
        while (b - a > 1) {
            c = (a + b) / 2;
            A = cross(l[a] - g, p - l[a]);
            C = cross(l[c] - g, p - l[c]);
            if (cross(l[a] - g, l[c] - g) >= 0) {
                if (A > -EPS&&C < -EPS)b = c;
                else a = c;
            }
            else {
                if (C < -EPS || A > -EPS)b = c;
                else a = c;
            }
        }
        return(cross(l[b%l.size()] - l[a], p - l[b%l.size()]) > -EPS);
    }

        //not necessary?
    IL D convex_area(Poly& l) {
        double res = 0;
        int n = l.size();
        FOR(i,2,n)
            res += (abs(cross(l[i - 1] - l[0], l[i] - l[i - 1]))) / 2.0;
        return res;
    }
    IL D area(Poly& l){
        double res=0;
        int n=l.size();
        REP(i,n)res+=cross(l[i],l[(i+1)%n]);
          return abs(res)/2.0;
    }
    inline vector<L> tangent_line(C c, P p) {
        vector<L> res;
        DCc(cp,r,c);
        P v = p - cp;
        D dist = abs(v);
        if (dist - r > -EPS) {
            double _cos = r / dist;
            double _sin = sqrt(1.0 - _cos*_cos);
            v = v * (r / dist);
            {
                P e = P(_cos * v.X - _sin * v.Y, _sin*v.X + _cos*v.Y);
                res.push_back({p, cp + e});
            }
            if(dist-r > EPS){
                P e = P( _cos*v.X + _sin*v.Y ,-_sin*v.X + _cos*v.Y );
                res.push_back({p, cp + e});
            }
        }
        return res;
    }
    IL vector<L> inner_common_tangent_line(C p, C q) {
        vector<L> res;
        DCc(Mp,Rp,p);
        DCc(Mq,Rq,q);
        D dist = abs(Mp - Mq);
        if (dist - (Rp + Rq) > -EPS) {
            P mid = (Mq*Rp + Mp*Rq) / (Rp + Rq);
            res = tangent_line(p, mid);
        }
        return res;
    }
    inline vector<L> outer_common_tangent_line(C p, C q) {
        vector<L> res;
        DCc(Mp,Rp,p);
        DCc(Mq,Rq,q);
        P v = Mp - Mq;
        D dist = abs(v);
        if (dist - abs(Rp - Rq) >- EPS) {
            if (abs(Rp - Rq) < EPS) {
                P e = v*P( 0, 1 );
                e = e / dist;
                res.pb(L(Mp + e, Mq + e));
                res.pb(L(Mp - e, Mq - e));
            }
            else {
                P mid = Mp + (Mq - Mp) * Rp / (Rp - Rq);
                res = tangent_line(p, mid);
            }
        }
        return res;
    }

     vector<Poly> decomposition(Poly p){
        int n = p.size();
        vector<Poly> res;
        while(n>=3){
            [&](){
                FOR(i, 0, n){
                    P a = p[i];
                    P b = p[(i+1)%n];
                    P c = p[(i+2)%n];
                    if (ccw(a,b,c)<0)continue;
                    if([&](){
                            FOR(j,3,n){
                                P d=p[(i+j)%n];
                                if(ccw(a,b,d)>-EPS&&ccw(b,c,d)>-EPS&&ccw(c,a,d)>-EPS)
                                    return true;
                            }
                            return false;
                        }()
                        )continue;
                    Poly nxt;
                    REP(j,n)if((i+j)%n!=(i+1)%n)nxt.push_back(p[(i+j)%n]);
                    swap(p,nxt);
                    res.push_back({a,b,c});
                    n--;
                    return;
                }
            }();
        }
        return res;
    }
    int in_triangle(P p,Poly q){
        REP(i,3)if(abs(p-q[i])<EPS)return 3;//on point
        REP(i,3){
            int s=sgn(q[i],q[(i+1)%3],p);
            if(s!=1){
                if(s==0)return 2;//on line
                else return 0; // not in
            }
        }
        return 1; // inside triangle
    }
    int in_C(P q,C c){
        DCc(p,r,c);
        if(abs(r-abs(p-q))<EPS)return 2; //on
        return r-abs(p-q)>-EPS ? 1:0;
    }
    int is_triangle_C(Poly t,C c){
        DCc(p,r,c);
        int cnt=0;
        REP(i,3)
            cnt+=(in_C(t[i],c)>0);
        if(cnt==3)return 3; // t in c
        if(cnt==0){
            double d=distance_P_LS(p,LS(t[2],t[0]));
            REP(i,2)
                d=min(d,distance_P_LS(p,LS(t[i],t[i+1])));
            if(r-d>-EPS)return 1; //intersect