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())

    edge = [[] for _ in range(n + 1)]
    for _ in range(m):
        a, b = map(int, input().split())
        a -= 1
        b -= 1
        edge[a].append([2 * (b - a) - 1, b])
    for i in range(n - 1):
        edge[i].append([2, i + 1])

    ans = dijkstra(edge, 0)[n - 1]
    print(ans)


if __name__ == "__main__":
    main()