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  1. #include <stdio.h>
  2.  
  3. int main(void) {
  4. int n,a=2,sum=2;
  5. scanf("&d",&n);
  6. do{
  7. n=n-1;
  8. a=a*3;
  9. sum=sum+a;
  10. }while(n>0);
  11. printf("%d",sum);
  12. return 0;
  13. }
  14.  
Success #stdin #stdout 0s 5324KB
stdin
3
stdout
2083039914