Given the following code, what is the return value when gas = [2, 3, 4] and cost = [3, 4, 3]?

Given the following code, what is the return value when gas = [2, 3, 4] and cost = [3, 4, 3]?

def canCompleteCircuit(gas, cost):
    n = len(gas)
    net = [gas[i] - cost[i] for i in range(n)]
    if sum(net) < 0:
        return -1
    prefix = [0] * (2 * n + 1)
    for i in range(2 * n):
        prefix[i+1] = prefix[i] + net[i % n]
    for i in range(n):
        if prefix[i+n] - prefix[i] >= 0:
            return i
    return -1

print(canCompleteCircuit(gas, cost))