#include <iostream>
#include <cstdio>
#include <cmath>
#include <map>

using namespace std;

map<int, int> scape;

int main()
{
	double total;
	int xtotal;
	int i, x, y;
	double dx, dy;
	map<int, int>::reverse_iterator iter, iter2;
	double miny;
	double b2, a, b, a2;

	cin >> xtotal;

	for (i = 0; i < xtotal; i++) {
		cin >> x >> y;
		scape[x] = y;
	}

	miny = 0;
	total = 0;
	for (iter = scape.rbegin(); iter != scape.rend(); iter++) {
		if (iter->second <= miny) {
			continue;
		}

		iter2 = iter;
		iter2--;
		dy = iter->second - miny;
		a = iter->second - iter2->second;
		b = iter2->first - iter->first;
		a2 = miny - iter2->second;
		b2 = (a2 * b) / a;
		dx = b - b2;
		total += sqrt((dx * dx + dy * dy));

		miny = iter->second;
	}

	printf("%0.2lf\n", total);

	return 0;
}