#include<cstdio>

using namespace std;

int N;

struct str
{
    int v[1009];
}dp[3];

void finish (str &x, int t)
{
    while (t)
        x.v[++x.v[0]] = t % 10, t /= 10;
}

str get (int x)
{
    str ans;
    ans.v[0] = 0;
    while (x)
        ans.v[++ans.v[0]] = x % 10, x /= 10;
    return ans;
}

str suma (str a, str b)
{
    str ras;
    if (a.v[0] > b.v[0]) ras.v[0] = a.v[0];
    else ras.v[0] = b.v[0];

    int t = 0;
    for (int i=1; i<=ras.v[0]; i++)
    {
        int c1 = 0, c2 = 0;
        if (i <= a.v[0]) c1 = a.v[i];
        if (i <= b.v[0]) c2 = b.v[i];
        ras.v[i] = (c1 + c2 + t) % 10;
        t = (c1 + c2 + t) / 10;
    }
    finish (ras, t);
    return ras;
}

void afis (str x)
{
    if (x.v[0] == 0)
        printf ("0");
    for (int i=x.v[0]; i>=1; i--)
        printf ("%d", x.v[i]);
    printf ("\n");
}

int main ()
{
freopen ("nunta.in", "r", stdin);
freopen ("nunta.out", "w", stdout);

scanf ("%d", &N);
dp[0] = dp[1] = get (1);
for (int i=2; i<=N; i++)
    dp[i % 3] = suma (dp[(i-1) % 3], dp[(i-2) % 3]);
afis (dp[N % 3]);

return 0;
}