#include<iostream>

#include<algorithm>

#include<cstdio>

#include<stdio.h>

#include<string.h>

#include<queue>

#include<cmath>

#include<map>

#include<set>

#include<vector>

using namespace std;

typedef long long ll;

const int maxn = 1e3 + ;

const ll mod = 1e8 + ;

struct node{

    ll x, y;

}p[maxn];

int mp[maxn][maxn], turn_num, vis[maxn][maxn][], nn, mm;

ll x[maxn], y[maxn];

int dir[][] = {, , , -, -, , , };

//下，左，上，右

bool dfs(int xx, int yy, int turn){ //将要朝向turn

    if(vis[xx][yy][turn]) return false;

    vis[xx][yy][turn] = ;

    int xxx = xx + dir[turn][], yyy = yy + dir[turn][];

    if(xxx <  || xxx > nn -  || yyy <  || yyy > mm - )

        return true;

    while(mp[xxx][yyy] != ){

        if(vis[xxx][yyy][turn]) return false;

        vis[xxx][yyy][turn] = ;

        xxx += dir[turn][];

        yyy += dir[turn][];

        if(xxx <  || xxx > nn -  || yyy <  || yyy > mm - )

            return true;

    }

    turn_num++;

    return dfs(xxx - dir[turn][], yyy - dir[turn][], (turn + ) % );

}

int main(){

    int n, sx, sy;

    while(scanf("%d", &n) != EOF){

        turn_num = ;

        memset(mp, , sizeof(mp));

        memset(vis, , sizeof(vis));

        for(int i = ; i < n; i++){

            scanf("%lld%lld", &p[i].x, &p[i].y);

            x[i] = p[i].x;

            y[i] = p[i].y;

        }

        x[n] = , y[n] = , p[n].x = , p[n].y = ;

        n++;

        sort(x, x + n);

        sort(y, y + n);

        int num1 = unique(x, x + n) - x;

        int num2 = unique(y, y + n) - y;

        for(int i = ; i < n; i++){

            int X, Y;

            X = lower_bound(x, x + num1, p[i].x) - x;

            Y = lower_bound(y, y + num2, p[i].y) - y;

            if(p[i].x ==  && p[i].y == ){

                sx = X, sy = Y;

            }

            else{

                mp[X][Y] = ;

            }

        }

        nn = num1, mm = num2;

        bool flag = dfs(sx, sy, );

        if(flag) printf("%d\n", turn_num);

        else printf("-1\n");

    }

    return ;

}

/*

4

1 0

0 1

0 -1

-1 0

*/