"use strict";
function Main(input) {
    let cin = new Inputer(input);
    let N = cin.getInt();
    let A0 = new Array(N);
    let A1 = new Array(N);
    for (let n = 0; n < N; n++) A0[n] = cin.getInt();
    for (let n = 0; n < N; n++) A1[n] = cin.getInt();
    for (let n = 1; n < N; n++) {
        A0[n] += A0[n - 1];
        A1[N - n - 1] += A1[N - n];
    }
    let ans = 0;
    for (let n = 0; n < N; n++) {
        let s = A0[n] + A1[n];
        if (ans < s) ans = s;
    }
    console.log(ans);
}
class Inputer{constructor(t){if(typeof t=='undefined')throw new Error('引数（stdin）を省略できません！');this.cnt=0;this.items=t.split(/\n|\s/)}getInt(){return this.items[this.cnt++]-0}getIntArray(t){if(typeof t=='undefined')throw new Error('引数（1以上）を省略できません！');if(t<1)throw new Error('引数は1以上であること！');let r=new Array(t);for(let e=0;e<t;e++)r[e]=this.getInt();return r}getStr(){return this.items[this.cnt++]}getStrArray(t){if(typeof t=='undefined')throw new Error('引数（1以上）を省略できません！');if(t<1)throw new Error('引数は1以上であること！');let r=new Array(t);for(let e=0;e<t;e++)r[e]=this.getStr();return r}}
if (typeof window == "undefined") Main(require("fs").readFileSync("/dev/stdin", "utf8"));