#include <bits/stdc++.h>
using namespace std;
 
struct Point {
    double x, y;
};
Point a[100005];
int n;
void init() {
    cin >> n;
 
}
 
void solve() {
    for (int i = 0; i < n; i++) {
        cin >> a[i].x >> a[i].y;
    }
 
    double chuVi = 0;
    for (int i = 0; i < n; i++) {
        int j = (i + 1) % n;
        double dx = a[i].x - a[j].x;
        double dy = a[i].y - a[j].y;
        chuVi += sqrt(dx * dx + dy * dy);
    }
 
    cout << fixed << setprecision(6) << chuVi;
}
 
int main() {
    init();
    solve();
    return 0;
}
 

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4
0 0
1 0
0 1
1 1