#include<stdio.h>

main()
{

    int n, a, b;
    int weight;

    while (scanf("%d", n) != EOF || scanf("%d", a) != EOF || scanf("%d",b) != EOF)
    {
        weight = n*a*b * 2;
        printf("%d", weight);
    }

    return 0;
}

1. You should specify the return type value for the main function: int main() {}
2. Is not necessarry to read the input data until the end of stream. Just read it one time:

int n, a, b, w;
scanf("%d%d%d", &n, &a, &b);
w = n*a*b*2;
printf("%d\n", w);

Please read scanf documentation. It returns count of read variables.
Also - task description means 3 and only 3 integers to read. Why did you use "while" here?

The main problem is in "||". You should use "&&" anyway. Otherwise, the shortpath magic happens.