#include<bits/stdc++.h>
// #define int long long
#define reg register
inline int read(){
	int k=1,x=0;char ch=getchar();
	while (ch<'0'||ch>'9') {if (ch=='-') k=-1; ch=getchar();}
	while (ch>='0'&&ch<='9') x=(x<<3)+(x<<1)+ch-48,ch=getchar();
	return k*x;
}
const int N=210,V=100;
int n,fa[N*N],ID[N][N],idx;
struct Node{int x,y;}p[N];
int find(reg int x){return fa[x]==x?x:fa[x]=find(fa[x]);}
inline void merge(reg int x,reg int y){
	x=find(x),y=find(y);
	if (x!=y) fa[x]=y;
}
signed main(){
	n=read();
	for (reg int i=1;i<=n;i++) p[i].x=read(),p[i].y=read();
	for (reg int i=-V;i<=V;i++) for (reg int j=-V;j<=V;j++) ID[i+V][j+V]=++idx;
	for (reg int i=1;i<=idx;i++) fa[i]=i;
	for (reg int x=-V*2;x<=V*2;x++) for (reg int y=-V*2;y<=V*2;y++){
		reg int now=0;
		for (reg int i=1;i<=n;i++){
			reg int X=x+p[i].x,Y=y+p[i].y;
			if (X<-V||X>V||Y<-V||Y>V) break;
			reg int nw=ID[X+V][Y+V];
			if (!now) now=nw; else merge(now,nw);
		}
	}
	reg int ans=0;
	for (reg int i=1;i<=idx;i++) ans+=find(i)==i;
	printf("%d\n",ans==idx?-1:ans);
	return 0;
}