cp230.cpp

#include <cstdio>

int main()
{
    int n, m, a, b;
    bool fire[1001] = {false};
    scanf("%d%d", &n, &m);
    while (m--)
    {
        scanf("%d%d", &a, &b);
        fire[a] = true;
        fire[b] = true;
    }
    int x = 1;
    while (fire[x])
    {
        x++;
    }
    printf("%d\n", n - 1);
    for (int i = 1; i < x; ++i)
    {
        printf("%d %d\n", i, x);
    }
    for (int i = x + 1; i <= n; ++i)
    {
        printf("%d %d\n", x, i);
    }
    return 0;
}