export {};

const input: number[] = require("fs").readFileSync(0,"utf8").toString().trim().split('\n').map(Number);
const N:number = input[0];
if(N<=3){
    console.log(N===1 ? input[1] : N===2 ? input[1]+input[2] : Math.max(input[1]+input[3], input[2]+input[3]));
}
else{
    let score: number[] = new Array(N+1).fill(0);
    score[1] = input[1];
    score[2] = input[1]+input[2];
    score[3] = Math.max(input[1]+input[3], input[2]+input[3]);
    score.forEach((_,i,arr) => {
        if(i>3){
            arr[i] = Math.max(arr[i-2]+input[i], arr[i-3] + input[i-1] + input[i]);
        }
    });
    console.log(score[N]);
}