#!/usr/bin/perl
use bigint;

while(defined(my $line=<STDIN>)){
    chomp $line;
    $N = $line;
    printP($N);
}

sub printP {
    ($N) = @_;
    my @A = ();
    $A[0][0] = 2; $A[0][1] = 1;
    $A[1][0] = 1; $A[1][1] = 1;
    my @R = ();
    $R[0][0] = 1; $R[0][1] = 0;
    $R[1][0] = 0; $R[1][1] = 1;
    my $P = 0;

    foreach(1..$N){
        if($_ & 1){
            @R = multMat(\@A, \@R);
            $P += $R[0][0];
        }
    }
    print "$P\n";
}

sub multMat {
    my ($A, $B) = @_;
    my @C = ();
    foreach my $i (0..1) {
        foreach my $j (0..1) {
            $C[$i][$j] = 0;
        }
    }
    foreach my $i (0..1) {
        foreach my $j (0..1) {
            foreach my $k (0..1) {
                $C[$i][$j] += ($A->[$i][$k] * $B->[$k][$j]);
            }
        }
    }
    return @C;
}