segmentation fault problem.

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

void main()
{
    int i=0,j,k,x,count=0,n=0,m=13,p=0,q=13;
    float s=0.0,dis=0.0;
    float * avg;
    float ** a;
    float ** b;
    char buf[BUFSIZ];
    FILE *fp1,*fp2,*fp3,*fp4;
    clrscr();
    fp1=fopen("a1.txt","r");
    fp2=fopen("a2.txt","r");
    fp3=fopen("result.txt","wb");
    while (fgets(buf,sizeof(buf),fp1) != NULL)
    n++; // counting rows of a1.txt

    while (fgets(buf,sizeof(buf),fp2) != NULL)
    p++;    // counting rows of a2.txt
    rewind(fp1);

    for(i=0;i<n;i++)
    {    a[i] = (float*) malloc(n * m * sizeof(float));
        for(j=0;j<m;j++)
        {

            fscanf(fp1,"%f",&a[i][j]);
        }
           printf("\n");
    }
    printf("\n");
    rewind(fp2);

    for(i=0;i<p;i++)
    {      b[i] = (float *) malloc(p * q * sizeof(float));
        for(j=0;j<q;j++)
        {
            fscanf(fp2,"%f",&b[i][j]);
        }
        printf("\n");
    }
          printf("\n");
    //calculation part
    avg = (float *) malloc(n * sizeof(float));
     for(x=0;x<=(n-1);x++)
     {
     if(count!=(n-p)+1){
        i=x;k=0;
        while(i<(p+x))
        {
            for(j=0;j<q;j++)
            {
                s=s+pow((a[i][j]-b[k][j]),2.0);

            }
                dis=dis+sqrt(s);


            s=0;
            i++;
            k++;

        }
        count++;
            avg[i]=dis;
            fprintf(fp3,"%f\n",avg[i]);
        dis=0;
     }
     else
     break;
    }

    getch();
    fclose(fp1);
    fclose(fp2);
    fclose(fp4);
    fclose(fp3);
    free(a);
    free(b);
    free(avg);
}