                        #include <bits/stdc++.h>
                        #include<iostream>
                        #include<cstdio>
                        #include<vector>
                        #include<queue>
         
                        #include<map>
                        #include<cstring>
                        #include<string>
                        #include <math.h>
                        #include<algorithm>
                        #include<functional>
                   #define int long long
                        #define inf  1000000007
                        #define pa pair<int,int>
        //        #define ll long long
                        #define pal pair<ll,ll>
                        #define ppa pair<pa,pa>
                        #define mp make_pair
                        #define EPS (1e-10)
                        #define equals(a,b) (fabs((a)-(b))<EPS)
                 
                        using namespace std;
                 
                        class Point{
                        	public:
                        	double x,y;
                        	Point(double x=0,double y=0):x(x),y(y) {}
                        	Point operator + (Point p) {return Point(x+p.x,y+p.y);}
                        	Point operator - (Point p) {return Point(x-p.x,y-p.y);}
                        	Point operator * (double a) {return Point(x*a,y*a);}
                        	Point operator / (double a) {return Point(x/a,y/a);}
                        	double absv() {return sqrt(norm());}
                        	double norm() {return x*x+y*y;}
                        	bool operator < (const Point &p) const{
                        		return x != p.x ? x<p.x: y<p.y;
                        	}
                        	bool operator == (const Point &p) const{
                        		return fabs(x-p.x)<EPS && fabs(y-p.y)<EPS;
                        	}
                        };
                        typedef Point Vector;
                 
                        struct Segment{
                        Point p1,p2;
                        };
                 
                    double hen(Vector a){
                    if(fabs(a.x)<EPS && a.y>0) return acos(0);
                    else if(fabs(a.x)<EPS && a.y<0) return 3*acos(0);
                    else if(fabs(a.y)<EPS && a.x<0) return 2*acos(0);
                    else if(fabs(a.y)<EPS && a.x>0) return 0.0;
                    else if(a.y>0) return acos(a.x/a.absv());
                    else return 2*acos(0)+acos(-a.x/a.absv());
                 
                    }
                 
                        double dot(Vector a,Vector b){
                        	return a.x*b.x+a.y*b.y;
                        }
                        double cross(Vector a,Vector b){
                        	return a.x*b.y-a.y*b.x;
                        }
                        int dx[4] = {1, 0, -1, 0};
                        int dy[4] = {0, 1, 0, -1};
        
                        //----------------kokomade temple------------
vector<int> G[100030];
  int n,k;
  int a[100020];
  int ra[100020];
int sumi[100020]={0};
  
  int N=262144;
pa sgt[530000];

pa minis(int i,int j ){
if(i==j) return sgt[i];
	else if(i%2==1){
		pa z=minis(i+1,j);
		if(sgt[i].first<z.first)return sgt[i] ;
		else return z;
	}
		else if(j%2==0) 	{
		pa z=minis(i,j-1);
		if(sgt[j].first<z.first)return sgt[j] ;
		else return z;
	}
else return minis(i/2,j/2);
}

pa sgtmin(int i ,int j){
	return minis(i+N,j+N);
}

void upd(int x,int y){
	x+=N;
sgt[x].first=y;
	sgt[x].second=x;
x=x/2;
while(x != 0){
	if(sgt[2*x+1].first<sgt[2*x].first){
		sgt[x]=sgt[2*x+1];
	}
	else sgt[x]=sgt[2*x];

x=x/2;
}
}

  
  
void saiki(int i){
	int y=G[i].size();
	for(int j=0;j<y;j++){
		ra[G[i][j]] = ra[i]+1;
		saiki(G[i][j]);
	}
}
  
void sai0(int i){
	sumi[i]=1;
//	cout<<"sai"<<" "<<i<<endl;
	upd(i,0);
	ra[i]=0;
	int y=G[i].size();
	for(int j=0;j<y;j++){
		if(sumi[G[i][j]]==1) continue;
	//	ra[G[i][j]] =0;
	//	upd(G[i][j],0);
		sai0(G[i][j]);
	//	sumi[G[i][j]]=1;
	}
	
}
  
  
      signed main(){
      cin>>n;
      	if(n%2==0) cout<<-1<<endl;
      	else cout<n-1<<endl;
return 0;
      }