local n=io.read("*n")
local dp={}
for i=0,n do
    dp[i]=0
end
dp[1],dp[2]=1,1
for i=0,n do
    if i+1<=n then
        dp[i+1]=dp[i+1]+dp[i]
    end
    if i+2<=n then
        dp[i+2]=dp[i+2]+dp[i]
    end
end
print(dp[n])