Cannot convert 'point' to 'point' - C (СИ)

#include<stdio.h>
#include<math.h>
float dlinna(struct point,struct point);
void main()
{
    struct point
    {
    int x,y;
    };
    struct point A,B,C;
    float AB,BC,CA,P;
    puts("Vvedite A(x;y), B(x;y), C(x;y)");
    scanf("%i %i %i %i %i",&A.x,&A.y,&B.x,&B.y,&C.x,&C.y);
    AB=dlinna(A,B);
    BC=dlinna(B,C);
    CA=dlinna(C,A);
    P=AB+BC+CA;
    printf("P = %f",P);
}
float dlinna(struct point x,struct point y)
{
    float z;
    z=sqrt((X.x*X.x-Y.y*X.x)*(X.x*X.x-Y.y*X.x)+(X.x*Y.y-Y.y*Y.y)*(X.x*Y.y-Y.y*Y.y));
    return(z);
}