int equi ( int A[], int n ) {
    int i=0;
    int SUMA = ((A[0]+A[n-1])*A[n-1])/n;
    int SUMA1=0,SUMA2=0;
    char flaga=1;
    if(SUMA==0)
    {
        if(A[0]==0) return 0;
        if(A[n-1]==0) return(n-1);
    }
    for(i=0;i<n;i++)
    {
        if(i==0)
        {
            SUMA1=A[0];
            SUMA2=((A[1]+A[n-1])*A[n-1])/n-1;
        }
        else
        {
            if(i==1)
            {
                SUMA1=((A[0]+A[i-1])*A[i-1])/i;
                SUMA2=((A[i+1]+A[n-1])*A[n-1])/n-1-i;
            }
            else
            {
                if(i<n-2){
                SUMA1=((A[0]+A[i-1])*A[i-1])/i-1;
                SUMA2=((A[i+1]+A[n-1])*A[n-1])/n-1-i;
                }
                else
                {
                    SUMA1=((A[0]+A[i-1])*A[i-1])/i-1;
                    SUMA2=A[n-1];
                }
            }
        }
        if(SUMA1==SUMA2)
            return(i);
        if(SUMA1!=SUMA2)
            flaga=0;
    }
        if(flaga==0)
        return(-1);
}