SGU - 123 - The sum （简单数学！）

SGU - 123 The sum Time Limit: 250MS   Memory Limit: 4096KB   64bit IO Format: %I64d & %I64u Submit Status Description Here is your second problem, keep calm and solve it . Nacci sequence of numbers is known to all : F1 = 1; F2 = 1; Fn+1 = Fn + Fn-1, for n>1. You have to find S - the sum of the first K Nacci numbers.   Input First line contains natural number K (0<K<41).   Output First line should contain number S.   Sample Input 5   Sample Output 12 Source

简单数学求和题，，居然int都不会爆，，刚开始我还以为要long long。。

AC代码：

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#define LL long long
using namespace std;

int a[42] = {0,1,1};

int main()
{
	int k;
	for(int i=3; i<41; i++)
	{
		a[i] = a[i-1] + a[i-2];
	}	
	scanf("%d", &k);
	int ans = 0;
	for(int i=1; i<=k; i++)
	{
		ans += a[i];
	}
	printf("%d\n", ans);
	return 0;
}