#include <stdio.h>
int main()
{
int n;
int i;
int m;
int count;
int dp[50];
while(scanf("%d",&n)!=EOF)
dp[1]=1;
dp[2]=1;
dp[3]=2;
while(n--)
count=0;
scanf("%d",&m);
for(i=4; i<=m; i++)
dp[i]=dp[i-1]+dp[i-2];
}
printf("%d\n",dp[m]);
return 0;