Energy Conversion

#include<iostream>
using namespace std;
int main(){
    int T;
    long long N,M,V,K;
    cin>>T;
    while(T--){
        int k=0;
        cin>>N>>M>>V>>K;
        if(M>=N) k=0 ;
        else{
            if((M-V)*K<=M) k=-1;
            else{
                while(M<N){
                    M=(M-V)*K;
                    k++;
                }
            }
        }
        cout<<k<<endl;
    }
    return 0;
}