
const Release = function () {
    const fs = require('fs');
    const stdin = function (text) {
        if (text) console.log(text);
        return fs.readFileSync('/dev/stdin', 'utf8');
    }
    return stdin;
};


const debug = false;

const stdin = debug ? Debug() : Release();
const input = stdin().split('\n');

const N = parseInt(input[0]);
const A1 = input[1].split(' ').map(x => parseInt(x));
const A2 = input[2].split(' ').map(x => parseInt(x));

const result = [];
for(var i = 0; i<N; i++) {
    var n = 0;
    A1.filter((x, j) => j <= i).map(x => n += x);
    A2.filter((x, j) => j >= i).map(x => n += x);
    result.push(n);
}

console.log(Math.max.apply(null, result));