# use strict;
# use warnings;

chomp(my $x = <>);
my $N = (split(/ /, $x))[0];
my @c = reverse(1 .. $N);
if ($N != 1) {
    chomp(my $y = <>);
    my @As = split(/ /, $y);
    foreach (@As) {
        push(@c, splice(@c, -$_, 1));
    }
}
print($c[-1], "\n");