#include <algorithm>
#include <functional>

#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>

#include <string>
#include <vector>

using namespace std;

typedef pair< int, int > point;
#define X first
#define Y second

int n;

vector< point > A;

inline long long ccw( point A, point B, point C ) { 
    long long sum = 0;

    sum += A.X * ( B.Y - C.Y );
    sum += B.X * ( C.Y - A.Y );
    sum += C.X * ( A.Y - B.Y );
    
    if( sum > 0 ) return +1;
    if( sum < 0 ) return -1;
    return 0;
}

int main( void )
{
    scanf( "%d", &n );
    A.resize( n );

    for( int i = 0; i < n; ++i ) 
        scanf( "%d %d", &A[i].X, &A[i].Y );

    int work = 2;

    for( int i = work; i < n; ++i ) {
        while( work >= 2 && ccw( A[work-2], A[work-1], A[i] ) > 0 ) --work;
        A[ work++ ] = A[i];
    }
    
    double sum = 0;

    for( int i = 1; i < work; ++i ) {
        long long dx = A[i].X - A[i-1].X;
        long long dy = A[i].Y - A[i-1].Y;
        sum += sqrt( double( dx*dx + dy*dy ) );
    }

    printf( "%.2lf\n", sum );
    return (0-0);
}