#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <queue>
#define int long long
using namespace std;
int read(){
	int x=0,f=1;char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
	return x*f;
}
const int N = 1e4+5;
int n;
int f[N][2][2];
signed main(){
	n = read();
	f[0][1][0] = f[0][1][1] = f[0][0][1] = 1e9;
	for(int i=1;i<=n;i++){
		int x,y;
		x = read()&1;y = read()&1;
		for(int j=0;j<=1;j++){
			for(int k=0;k<=1;k++){
				f[i][j][k] = f[i-1][j^x][k^y];
			}
		}
		swap(x,y);
		for(int j=0;j<=1;j++){
			for(int k=0;k<=1;k++){
				f[i][j][k] = min(f[i][j][k],f[i-1][j^x][k^y]+1);
			}
		}
	}
	if(f[n][0][0]>n){
		cout<<-1<<"\n";
		return 0;
	}
	cout<<f[n][0][0]<<"\n";
	return 0;
}