const main = ls => {
    const n = Number(ls[0])
    const V = ls[1].split(" ").map(Number)
    const Arr = [];
    for (let i = 0; i < n; i++) {
        let num = -1;
        if(i+2<n){
            let newArr = [];
            for (let j = 0; j < n-2-i; j++) {
                newArr.push(V[i+2+j])
            }
            num = Math.max(...newArr)+V[i]
        }
        Arr.push(num);
    }
    console.log(Math.max(...Arr))
}
 
main(require('fs').readFileSync('/dev/stdin', 'utf8').trim().split('\n'));