题解 | #小乐乐计算求和#

#include<stdio.h>
int f(int n) { 
    return n == 1 ? 1 : n * f(n - 1);
}
int main(void) {
    int n;
    scanf("%d", &n);
    int sum = 0;
    for (int i = 1; i <= n; i++)
        sum += f(i);
    printf("%d", sum);
    return 0;
}