#include <stdio.h>
int main(void) {
int a[50],i,sum;
a[0]=2;
a[1]=-1;
for(i=2,sum=0;i<=30;i++){
a[i]=-a[i-1]+a[i-2]+2;
if(i%4==0)
sum = sum + a[i];
}
return 0;
}
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