HDU 2046

思路：找递推关系a[n] = a[n-1]+a[n-2].

#include<stdio.h>
long long int a[51];
int main()
{
    int i,n;
    a[1] = 1;
    a[2] = 2;
    a[3] = 3;
    for(i = 3;i <= 50;i ++)
        a[i] = a[i-2]+a[i-1];
    while(~scanf("%d",&n))
        printf("%I64d\n",a[n]);
    return 0;
}