Weakened Common Divisor

http://codeforces.com/contest/1025/problem/B

#include<bits/stdc++.h>
using namespace std;
const int N=1.5e5+10;
set<int>s;
int n,a[N],b[N],m,f,ans;
int main(){
    set<int>::iterator it;
    scanf("%d",&n);
    for (int i=1;i<=n;i++){
        scanf("%d%d",&a[i],&b[i]);
    }
    m=sqrt(a[1]);
    for (int i=2;i<=m;i++){
        if (a[1]%i==0){
            s.insert(i);
            while (a[1]%i==0){
                a[1]=a[1]/i;
            }
        }
    }
    if (a[1]>1){
        s.insert(a[1]);
    }
    m=sqrt(b[1]);
    for (int i=2;i<=m;i++){
        if (b[1]%i==0){
            s.insert(i);
            while (b[1]%i==0){
                b[1]=b[1]/i;
            }
        }
    }
    if (b[1]>1){
        s.insert(b[1]);
    }
    for (it = s.begin(); it != s.end(); it++) {
        int i;
        for (i=2;i<=n;i++) {
            if (a[i] % (*it) !=0 && b[i]%(*it) !=0) {
                break;
            }
        }
        if (i>n){
            f=1;
            printf("%d\n",*it);
            break;
        }
    }
    if (!f) {
        printf("-1\n");
    }
}