#include <bits/stdc++.h>
using namespace std;
#define all(c) (c).begin(),(c).end()
#define rrep(i,n) for(int i=(int)(n)-1;i>=0;i--)
#define REP(i,m,n) for(int i=(int)(m);i<(int)(n);i++)
#define rep(i,n) REP(i,0,n)
#define iter(c) __typeof((c).begin())
#define tr(it,c) for(iter(c) it=(c).begin();it!=(c).end();it++)
#define pb(a) push_back(a)
#define pr(a) cout<<(a)<<endl
#define PR(a,b) cout<<(a)<<" "<<(b)<<endl
#define R cin>>
#define F first
#define S second
#define ll long long
bool check(int n,int m,int x,int y){return x>=0&&x<n&&y>=0&&y<m;}
const ll MAX=1000000007,MAXL=1LL<<60,dx[4]={-1,0,1,0},dy[4]={0,1,0,-1};
typedef pair<int,int> P;

int main() {
  P a[3];
  rep(i,3) cin >> a[i].F >> a[i].S;
  rep(i,3) {
    REP(j,i+1,3) {
      if(a[i].F==a[j].F) {
	int d=a[i].S/__gcd(a[i].S,a[j].S)*a[j].S;
	a[i].S=a[j].S=d;
      }
    }
  }
  int ans=-1;
  rep(i,3) {
    int d=a[i].F+a[i].S;
    if(ans==-1 || ans==d) ans=d;
    else ans=-2;
  }
  if(a[0].S==a[1].S && a[0].S==a[2].S) ans=a[0].F;
  if(ans<0) ans=-1;
  cout << ans << endl;
  return 0;
}