[求助] 如图所示，就卡在下面

program main
    implicit none
    real x1,x2,x3,x4,x5,x6,x7,x8,x9,x10,x11,x12,x13,x14,x15,x16,f1,f2,f3,f4,f5,f6,f7,f8,a,m,b,c,i
    integer x(1:6)
    print*,'请输入x1,x2,x3,x4,x5,x6,b:'
    read*,b
    do i=1,6
        read*,x(i)
    f1=x1-x2+2.0*x1*x1+2.0*x1*x2+x2*x2
    f2=x3-x4+2.0*x3*x3+2.0*x3*x4+x4*x4
    f3=x5-x6+2.0*x5*x5+2.0*x5*x6+x6*x6
    f4=max(f1,f2,f3)
    if (f4==f1) then
        x7=x1
        x8=x2
        x11=(x3+x5)/2.0
    x12=(x4+x6)/2.0
    else if (f4==f2)then
        x7=x3
        x8=x4
        x11=(x1+x5)/2.0
    x12=(x2+x6)/2.0
    else
        x7=x5
        x8=x6
        x11=(x3+x1)/2.0
    x12=(x4+x2)/2.0
    end if
    f5=min(f1,f2,f3)
    if (f5==f1) then
        x9=x1
        x10=x2
    else if (f5==f2) then
        x9=x3
        x10=x4
    else
        x9=x5
        x10=x6
    end if
    f6=x11-x12+2.0*x11*x12+2.0*x11*x11+x12*x12
    x13=2.0*x11-x7
    x14=2.0*x12-x8
    f7=x13-x14+2.0*x13*x13+2.0*x13*x14+x14*x14
    if (f7<f6) then
        x15=2.0*x13-x11
        x16=2.0*x14-x12
    else
        x15=0.5*x7+0.5*x11
        x16=0.5*x8+0.5*x12
    end if
        f8=x15-x16+2.0*x15*x15+2.0*x15*x16+x16*x16
        if (f8<f5) then
        x1=x1
        x2=x2
        x3=x15
        x4=x16 
        x5=x5
        x6=x6
        else 
            x1=x1
            x2=x2
            x3=x13
            x4=x14
            x5=x5
            x6=x6
        end if
        if (f8>f5.and.f8<f4) then
            x1=x1
            x2=x2
            x3=x3
            x4=x4
            x5=x15
            x6=x16
            end if
        m=(f1-f6)**2/3.0+(f8-f6)**2/3.0+(f3-f6)**2/3.0
        a=sqrt(m)
        if (a<b) exit
        end do
        print*,a
        end