Help me in solving SEQSEARCH problem

My issue

plz help what is wrong in this code

My code

#include <bits/stdc++.h>
using namespace std;
using ull= long long int;

ull solve(ull a,ull b,ull k){
    if(k==0)return 0;
    if(a>b){
        if(k%2==0)return (k/2)*b;
        return a+((k/2)-1)*b;
    }
    return (k-1)*b;
}
int main() {
	// your code goes here
    int t;
    cin>>t;
    while(t--){
        int t;
        ull a,b,k;
        cin>>a>>b>>k;
        cout<<solve(a,b,k)<<endl;
    }
}

Problem Link: Sequence Search Practice Coding Problem