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  1. #include <stdio.h>
  2.  
  3. int fib(int n) {
  4.     int i;
  5.     int a_1 = 0, a_2 = 1, a_3;
  6.     if(n==1)
  7.     return 0;
  8.     else if(n==2)
  9.     return 1;
  10.    for(i=3;i<n;i++){
  11.    	a_3=2*a_2+a_1+1;
  12.    	a_1=a_2;
  13.    	a_2=a_3;
  14.    }
  15.    return a_2;
  16. }
  17.  
  18. int main(void) {
  19.     int n;
  20.  
  21.     scanf("%d", &n);
  22.     printf("第 %d 項の値：%d\n", n, fib(n));
  23.     return 0;
  24. }
Success #stdin #stdout 0.01s 5276KB
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6
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第 6 項の値：20
https://ideone.com/Vkqt9k
language:
C (gcc 8.3)
created:
46 days ago
visibility:
public

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