20个点里有两个wa了，求大佬解释

#include<iostream>
using namespace std;
int main(){

    float s,x;
    float v=7;
    float d=0;
    cin>>s>>x;

    if(x*2>7)
    {
        cout<<"y"<<endl;
        return 0;
    }

    while(d<s-x)
    {
        v=v*0.98;
        d+=v;
    }

    if(d+v<s+x)
    {
        cout<<"y"<<endl;
        return 0;
    }

    cout<<"n"<<endl;
    return 0;
}