What does this Zig snippet output?

1const std = @import("std");
2pub fn main() void {
3    const matrix = [2][3]u8{
4        .{ 1, 2, 3 },
5        .{ 4, 5, 6 },
6    };
7    var sum: u32 = 0;
8    for (matrix) |row| {
9        for (row) |val| {
10            sum += val;
11        }
12    }
13    std.debug.print("{d}\n", .{sum});
14}