#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>

int max( int x, int y )
{
    if ( x > y ) {
        return x;
    } else {
        return y;
    }
}

int calc( int N, int* V )
{
    if ( N == 0 ) {
        return 0;
    } else if ( N == 1 ) {
        return V[0];
    } else {
        int ret1 = V[0] + calc( N-2, V+2 );
        int ret2 = calc( N-1, V+1 );
        return max( ret1, ret2 );
    }
}

int main()
{
    // input
    int N;
    int V[1000];
    scanf( "%d", &N );
    for ( int i=0; i<N; i++ ) {
        scanf( " %d", V+i );
    }

    // process
    int ret = calc( N, V );

    // output
    printf( "%d\n", ret );

    return 0;
}