#include <stdio.h>
#include <vector>
#include <queue>

using namespace std;

struct interv
{
    double start, end;

    bool operator>(const struct interv &other) const
    {
        if (start != other.start)
            return start > other.start;
        return end > other.end;
    }
};

int main()
{
    priority_queue<struct interv, vector<struct interv>, greater<struct interv> > heap;
    struct interv help;
    double len, ans;

    while (scanf (" %lf", &len) && len > 0)
    {
        ans = len;

        while (scanf (" %lf %lf", &help.start, &help.end) != EOF &&
                help.start <= help.end)
        {
            heap.push(help);
        }

        help = heap.top();
        heap.pop();
        while (!heap.empty())
        {

            if (heap.top().start > help.end)
            {
                //put it on the vector and ask for more
                ans -= help.end - help.start;
                help = heap.top();
            }
            else if (heap.top().end > help.end)
            {
                help.end = heap.top().end;
            }
            else
            {
            } //do nothing, subinterval is inside

            heap.pop();
        }
        ans -= help.end - help.start;

        printf("The total planting length is %.1lf\n", ans);
    }

    return 0;
}