SGU 123 The sum

SGU_123

    斐波那契数列前n项和为2*F(n+1)-F(n-1)-1。

#include<stdio.h>
#include<string.h>
long long int f[50];
int main()
{
    int i, j, k;
    f[0] = 0, f[1] = 1;
    for(i = 2; i <= 41; i ++)
        f[i] = f[i - 1] + f[i - 2];
    while(scanf("%d", &k) == 1)
        printf("%d\n", f[k + 1] - f[k - 1] - 1 + f[k + 1]);
    return 0;
}