int main() { double n; cin>>n; double l=0,r=n; if(n<=-1) swap(l,r); if(n>-1&&n<1)l=-1,r=1; while(r-l>=1e-8) { double mid=(l+r)/2; if(midmidmid<=n) l=mid; else r=mid; } printf(“%.6f”,l); return 0; }