#include <stdio.h>
int poslFib(const char *name, int *res);
int poslFib(const char *name, int *res)
{
    FILE*fp; double x, prev1=0,prev2=0; int opr=0;
    if (!(fp = fopen(name, "r")))
        return -1;
fscanf(fp, "%lf", &prev1);
if (prev1<=1 && prev1>=1)
    {
    opr=1;
    fscanf(fp, "%lf", &prev2);
    if (feof(fp))
    {
        fclose(fp);
        *res = opr;
        return 0;
    }
    else
       {


      if (prev2<=1 && prev2>=1)
        {
        while (fscanf(fp, "%lf", &x) == 1)
        {

         if (x > prev1 + prev2 || x < prev1 + prev2) opr=0;
           prev1 = prev2;
           prev2 = x;

        }
        }
      else opr=0;

       }


}
    if (!feof(fp))
    {
        fclose(fp);
        return -2;
    }
    fclose(fp);
    *res = opr;
    return 0;

}
int main(void)
{
    const char *fname = "a.txt";
    int answer; int ret;
    ret = poslFib(fname, &answer);
    if (ret < 0)
    {
        switch (ret)
        {
        case -1:
            printf("Cannot open %s\n", fname);
            break;
        case -2:
            printf("Cannot read %s\n", fname);
            break;
        default:
            printf("Error %d in file %s\n", ret, fname);

        }
        return 1;
    }
    printf("Fib = %d\n", answer);
    return 0;
}