UVA - 580 - Critical Mass (C solution)

//same algorithm as java solution

#include <stdio.h>

int main()
{   int cases,i;
    long add[31];
        add[3]=1;
        add[4]=2;
        add[5]=4;
        for( i=6;i<31;i++){
            add[i]=add[i-3]+add[i-2]+add[i-1];

        }

    long bg[31];
        bg[0]=0;
        bg[1]=0;
        bg[2]=1;
        for( i=3;i<31;i++){
            bg[i]=2*bg[i-1]+add[i];
        }

    while(1){
        scanf("%d",&cases);
        if(cases==0)
            break;
        printf("%ld\n",bg[cases-1]);
    }
       return 0;
}