b[1<<21],s,i,j;main(n){for(;~scanf("%d",&n)?b[n]=s,s=1:b[i]&&j<1e6?b[j+=i]?b[j]=b[j]>b[i]?b[j]:b[i]+1:0,s=s>b[j]?s:b[j]:(j=++i)<1e6;);s=!printf("%d",s);}