from heapq import heapify, heappop, heappush
from typing import List


def dijkstra(edges: "List[List[(cost, to)]]", start_node: int) -> list:
    hq = []
    heapify(hq)
    dist = [float("inf")] * len(edges)
    heappush(hq, (0, start_node))
    dist[start_node] = 0
    while hq:
        min_cost, now = heappop(hq)
        if min_cost > dist[now]:
            continue
        for cost, nxt in edges[now]:
            if dist[nxt] > dist[now] + cost:
                dist[nxt] = dist[now] + cost
                heappush(hq, (dist[nxt], nxt))
    return dist


def main():
    n, m = map(int, input().split())

    st = {0, n - 1}
    edge = []
    for _ in [0] * m:
        a, b = map(int, input().split())
        a -= 1
        b -= 1
        edge.append((a, b))
        st.add(a)
        st.add(b)

    lst = sorted(list(st))
    nn = len(lst)
    h = {x: i for i, x in enumerate(lst)}  # 座標圧縮

    route = [[] for _ in [0] * nn]
    for a, b in edge:
        route[h[a]].append([2 * b - 2 * a - 1, h[b]])
    for i in range(nn - 1):
        route[i].append([2 * (lst[i + 1] - lst[i]), i + 1])
    ans = dijkstra(route, 0)[-1]
    print(ans)


if __name__ == "__main__":
    main()