Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)

func scanBoard() [][]int {
	ret := make([][]int, 8)
	for k := range ret {
		ret[k] = make([]int, 8)
		for l := range ret[k] {
			ret[k][l] = 0
		}
	}
	for i := 0; i < 8; i++ {
		scanner.Scan()
		row := strings.Split(scanner.Text(), "")
		if reflect.DeepEqual(row, []string{}) {
			break
		}
		for j := 0; j < 8; j++ {
			ret[i][j], _ = strconv.Atoi(row[j])
		}
	}
	return ret
}

var emptyBoard = [][]int{{0,0,0,0,0,0,0,0},
						 {0,0,0,0,0,0,0,0},
						 {0,0,0,0,0,0,0,0},
	                     {0,0,0,0,0,0,0,0},
	                     {0,0,0,0,0,0,0,0},
	                     {0,0,0,0,0,0,0,0},
	                     {0,0,0,0,0,0,0,0},
	                     {0,0,0,0,0,0,0,0}}

func main() {
	for {
		var board [][]int
		var ans string
		if board = scanBoard(); reflect.DeepEqual(board, emptyBoard) {
			break
		}
		// fmt.Println(board)
		for i := 0; i < 7; i++ {
			for j := 0; j < 7; j++ {
				if board[i][j] == 1 && board[i+1][j] == 1 && board[i][j+1] == 1 && board[i+1][j+1] == 1 {
					ans = "A"
				}
			}
		}
		for i := 0; i < 5; i++ {
			for j := 0; j < 8; j++ {
				if board[i][j] == 1 && board[i+1][j] == 1 && board[i+2][j] == 1 && board[i+3][j] == 1 {
					ans = "B"
				}
			}
		}
		for i := 0; i < 8; i++ {
			for j := 0; j < 5; j++ {
				if board[i][j] == 1 && board[i][j+1] == 1 && board[i][j+2] == 1 && board[i][j+3] == 1 {
					ans = "C"
				}
			}
		}
		for i := 0; i < 6; i++ {
			for j := 0; j < 7; j++ {
				if board[i][j+1] == 1 && board[i+1][j] == 1 && board[i+1][j+1] == 1 && board[i+2][j] == 1 {
					ans = "D"
				}
			}
		}
		for i := 0; i < 7; i++ {
			for j := 0; j < 6; j++ {
				if board[i][j] == 1 && board[i][j+1] == 1 && board[i+1][j+1] == 1 && board[i+1][j+2] == 1 {
					ans = "E"
				}
			}
		}
		for i := 0; i < 7; i++ {
			for j := 0; j < 6; j++ {
				if board[i][j+1] == 1 && board[i][j+2] == 1 && board[i+1][j] == 1 && board[i+1][j+1] == 1 {
					ans = "G"
				}
			}
		}
		for i := 0; i < 6; i++ {
			for j := 0; j < 7; j++ {
				if board[i][j] == 1 && board[i+1][j] == 1 && board[i+1][j+1] == 1 && board[i+2][j+1] == 1 {
					ans = "F"
				}
			}
		}
		fmt.Println(ans)
	}
}

C++: #include <bits/stdc++.h>

#define rep(i, n) for (int i = 0; i < int(n); i++)
#define rrep(i, n) for (int i = int(n) - 1; i >= 0; i--)
#define reps(i, n) for (int i = 1; i <= int(n); i++)
#define rreps(i, n) for (int i = int(n); i >= 1; i--)
#define repc(i, n) for (int i = 0; i <= int(n); i++)
#define rrepc(i, n) for (int i = int(n); i >= 0; i--)
#define repi(i, a, b) for (int i = int(a); i < int(b); i++)
#define repic(i, a, b) for (int i = int(a); i <= int(b); i++)
#define repp(i, n) rep(i, n)
#define reppp(i, n) repp(i, n)
#define rrepp(i, n) rrep(i, n)
#define repss(i, n) reps(i, n)
#define repcc(i, n) repc(i, n)
#define repii(i, a, b) repi(i, a, b)
#define each(x, y) for (auto &x : y)
#define all(a) (a).begin(), (a).end()
#define bit(b) (1ll << (b))

using namespace std;

using i32 = int;
using i64 = long long;
using u64 = unsigned long long;
using f80 = long double;
using vi32 = vector<i32>;
using vi64 = vector<i64>;
using vu64 = vector<u64>;
using vf80 = vector<f80>;
using vstr = vector<string>;

inline void yes() { cout << "Yes" << '\n'; exit(0); }
inline void no() { cout << "No" << '\n'; exit(0); }
inline i64 gcd(i64 a, i64 b) { if (min(a, b) == 0) return max(a, b); if (a % b == 0) return b; return gcd(b, a % b); }
inline i64 lcm(i64 a, i64 b) { return a / gcd(a, b) * b; }
inline u64 xorshift() { static u64 x = 88172645463325252ull; x = x ^ (x << 7); return x = x ^ (x >> 9); }
void solve(); int main() { ios::sync_with_stdio(0); cin.tie(0); cout << fixed << setprecision(16); solve(); return 0; }
template <typename T> class pqasc : public priority_queue<T, vector<T>, greater<T>> {};
template <typename T> class pqdesc : public priority_queue<T, vector<T>, less<T>> {};
template <typename T> inline void amax(T &x, T y) { if (x < y) x = y; }
template <typename T> inline void amin(T &x, T y) { if (x > y) x = y; }
template <typename T> inline T power(T x, i64 n, T e = 1) { T r = e; while (n > 0) { if (n & 1) r *= x; x *= x; n >>= 1; } return r; }
template <typename T> istream& operator>>(istream &is, vector<T> &v) { each(x, v) is >> x; return is; }
template <typename T> ostream& operator<<(ostream &os, vector<T> &v) { rep(i, v.size()) { if (i) os << ' '; os << v[i]; } return os; }
template <typename T, typename S> istream& operator>>(istream &is, pair<T, S> &p) { is >> p.first >> p.second; return is; }
template <typename T, typename S> ostream& operator<<(ostream &os, pair<T, S> &p) { os << p.first << ' ' << p.second; return os; }

void solve() {
  using P = pair<int, int>;
  vector<vector<P>> target = {
    { P(0, 1), P(1, 0), P(1, 1) },
    { P(1, 0), P(2, 0), P(3, 0) },
    { P(0, 1), P(0, 2), P(0, 3) },
    { P(1, 0), P(1, -1), P(2, -1) },
    { P(0, 1), P(1, 1), P(1, 2) },
    { P(1, 0), P(1, 1), P(2, 1) },
    { P(0, 1), P(1, 0), P(1, -1) },
  };
  auto check = [](int x, int y) {
    if (x < 0 || x >= 8 || y < 0 || y >= 8) return false;
    return true;
  };

  while (true) {
    vstr board(8);
    rep(i, 8) if (!(cin >> board[i])) return;
    rep(i, 8) rep(j, 8) {
      if (board[i][j] == '0') continue;
      char ans;
      rep(l, target.size()) {
        auto t = target[l];
        bool f = true;
        rep(k, 3) {
          int wx = i + t[k].first;
          int wy = j + t[k].second;
          if (!check(wx, wy)) { f = false; break; }
          if (board[wx][wy] == '0') f = false;
        }
        if (f) {
          ans = 'A' + l;
          break;
        }
      }
      cout << ans << '\n';
      rep(i, 8) rep(j, 8) board[i][j] = '0';
    }
  }
}

C++: #include <iostream>
#include <cstdio>

#define rep(i,n) for(int i = 0 ; i < n ;i++ )
using namespace std;

int main(){
 char  ma[8][8];
  while(!cin.eof()){
    rep(i,8){
      rep(j,8){
ma[i][j]='0';
      }
    }
    rep(i,8){
      rep(j,8){
	cin >> ma[i][j];

      }
    }
    rep(i,8){
      rep(j,8){
	if(ma[i][j]=='1'){
	  if(ma[i][j+1] == '1' && ma[i+1][j+1] == '1'&& i+1 < 8&&j+1 < 8 ){
	    cout << 'A' << endl;
	    break;
	  }else if(ma[i+3][j] == '1' &&i+3 < 8){
	    cout << 'B' << endl;
	    break;
	  }else if(ma[i][j+3] == '1'&& j+3 < 8){
	    cout << 'C' << endl;
	    break;
	  }else if(ma[i+3][j-1] == '1' && i+3 < 8 && 0 < j-1){
	    cout << 'D' << endl;
	    break;
	  }else if(ma[i+1][j+3] == '1' && i+1<8 && j+3 < 8){
	    cout << 'E' << endl;
	    break;
	  }else if(ma[i+1][j+3] == '1' && i+1 < 8&& j+3 < 8){
	    cout << 'F' << endl;
	    break;
	  }else if(ma[i][j+1] == '1' && ma[i+1][j-1] == '1' && j+1 < 8 && i+1 < 8 && 0<j-1 ){
	    cout << 'G' << endl;
	  }
	}
      }
    }
  }
  
  return 0;
}