let road1 = [5, 4, 5, 8, 12, 9, 9, 3];
let road2 = [7, 3, 3, 12, 10, 2, 10, 7];

let min = 100000;
let rLength = road1.length;

let arrRoad1 = [];
let arrRoad2 = [];

let fromRoad1 = 0;
let fromRoad2 = 0;

for(let i = 0;i < rLength;i++) {
    fromRoad1 += road1[i];
    fromRoad2 += road2[rLength - i - 1];
    arrRoad1[i] = fromRoad1;
    arrRoad2[rLength - i - 1] = fromRoad2;
}

for(let i = 0; i < rLength;i++) {
    let c = arrRoad1[i] + arrRoad2[2];
    if(c < min) min = c;
}