import std.algorithm;
import std.array;
import std.conv;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

int readint() { return readln.chomp.to!int; }
int[] readints() { return readln.split.to!(int[]); }

int calc(int[][] xs) {
    int n = cast(int) xs[0].length;

    int ans = 0;
    for (int i = 0; i < n; i++) {
        int x = 0;
        for (int j = 0; j < n; j++) {
            if (j < i) x += xs[0][j];
            if (j == i) x += xs[0][j] + xs[1][j];
            if (j > i) x += xs[1][j];
        }
        ans = max(ans, x);
    }
    return ans;
}

void main() {
    readint;
    int[][] xs;
    xs ~= readints;
    xs ~= readints;

    int ans = calc(xs);
    writeln(ans);
}
