The sum

直接上代码.......

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#include<stdio.h>

const int MAXN = 41;

int main()
{
    long long Fib[MAXN] = {0, 1}, sum[MAXN]={0, 1};

    for(int i=2; i<MAXN; i++)
    {
        Fib[i] = Fib[i-1] + Fib[i-2];
        sum[i] = Fib[i] + sum[i-1];
    }

    int N;

    scanf("%d", &N);

    printf("%lld
", sum[N]);

    return 0;
}