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;}