#include <cstdio>
int a[1005],b[1005];
void add(int a[1005],int b[1005]){
    int t=0,i;
    for(i=1;i<=a[0] or i<=b[0] or t;++i,t/=10)
        a[i]=(t+=a[i]+b[i])%10;
    a[0]=i-1;
}

int main(){
    freopen("nunta.in", "r", stdin);
    freopen("nunta.out", "w", stdout);
    int n, i;
    a[0] = 1;
    a[1] = 1;
    b[0] = 1;
    b[1] = 2;
    scanf("%d", &n);
    if(n==1){printf("n"); return 0;}
    for(i=1;i<=n-2;++i){
        if(i&1) add(a,b);
        else add(b,a);
    }
    int x=i;
    if(x&1)
        for(i=b[0];i>=1;--i)
            printf("%d", b[i]);
    else
        for(i=a[0];i>=1;--i)
            printf("%d",a[i]);
    return 0;
}