#include<cstdio>
using namespace std;
short a[22],b[22],c[22];
int n;
void adun(short c[], short a[], short b[]){
    int t=0;
    for(int i=1; i<=c[0];++i) c[i]=0; c[0]=0;
    for(int i=0;i<=a[0];++i) c[i]=a[i];
    if(b[0]>c[0]){
        for(int i=a[0]+1;i<=b[0];) c[i++]=0;
        c[0]=b[0];
    }
    else for(int i=b[0]+1;i<=a[0];) b[i++]=0;
    for(int i=1;i<=c[0];i++){
        c[i]+=b[i]+t;
        t=c[i]/10;
        c[i]%=10;
    }
    if (t) c[++c[0]]=t;

}
void schimb(short a[], short b[]){
    for(int i=0;i<=b[0];++i) a[i]=b[i];
}
int main(){
    freopen("nunta.in","r",stdin); freopen("nunta.out","w",stdout);
    scanf("%d", &n);
    a[0]=1; a[1]=1;
    b[0]=1; b[1]=2;

    for(int i=3;i<=n;++i){
        adun(c,a,b);  //c=a+b
        schimb(a,b); //a=b;
        schimb(b,c); //b=c
    }
    if(n>3){
    for(int i=1; i<=c[0];++i) printf("%d", c[i]); printf("\n"); return 0;
    }
    else printf("%d\n", n);
    return 0;
}