#include <bits/stdc++.h>
using namespace std;
const int n=1e6+5;
vector<int>prime(n,true);
 
void sieve(){
    for (int p = 2; p * p <= n; p++) {
        if (prime[p] == true) {
            for (int i = p * p; i <= n; i += p)
                prime[i] = false;
        }
    }
}
 
 
 
int main()
{
    int q;cin>>q;
      sieve();
    vector<int>pre(n,0);
    for(int i=2; i<=n; i++){
        if(prime[i])pre[i]=pre[i-1]+1;
        else pre[i]=pre[i-1];
    }
    while(q--){
        int a,b,k;
        cin>>a>>b>>k;
        int ans=INT_MAX;
        int low=a-1,high=b+1,mid;
        while(low<high){
            mid=(low+high)/2;
            if(pre[mid]-pre[a-1]>=k){
                ans=min(ans,mid);
                high=mid;
            }
            else low=mid+1;
        }
        if(ans==INT_MAX || ans>b)ans=-1;
        cout<<ans<<endl;
 
 
    }
    return 0;
}