#include<stdio.h>int main(){ int r, c; char a[20][20]; while (scanf("%d %d", &r, &c), r && c) { getchar(); int i, j, index = 0; for (i = 0; i < r; i++) for (j = 0; j < c; j++) a[i][j] = getchar(); getchar(); int isRow = 1, isOrder = 1, rb = 0, re = c - 1, cb = 0, ce = r - 1; while (1) { if (isRow) { if (rb > re) break; if (isOrder) { for (i = rb; i <= re; i++) putchar(a[index][i] - 7); index = re; cb++; } else { for (i = re; i >= rb; i--) putchar(a[index][i] - 7); index = rb; ce--; } isRow = !isRow; } else { if (cb > ce) break; if (isOrder) { for (i = cb; i <= ce; i++) putchar(a[i][index] - 7); index = ce; re--; } else { for (i = ce; i >= cb; i--) putchar(a[i][index] - 7); index = cb; rb++; } isOrder = !isOrder; isRow = !isRow; } } putchar('n'); } return 0;}
