#include <stdio.h>
//正の奇数nを引数とし，以下の正の奇数の和を求める関数
 int rec(int n){
    if (n % 2 == 1){            // nが奇数のとき
        if (n == 1){
            return 1;
        }
        return n + rec(n - 2);  // 奇数だけ足す
    }
    else{                       // nが偶数のとき
        if (n == 2){
            return 2;
        }
        return n + rec(n - 2);  // 偶数だけ足す
    }
}
 
int main(void) {
    int n = 11;
    printf("%d以下の正の奇数の和は%d\n", n, rec(n));
	return 0;
}

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