#include<cstdio>
#include<cstring>
using namespace std;
const int MS=50;
int n,a[MS],b[MS],c[MS];
inline void add()
{   int i,t;
    for(i=1,t=0;i<=a[0]||i<=b[0]||t;++i,t/=10)
        c[i]=(t+=a[i]+b[i])%10;
    c[0]=i-1;
}
int main()
{   freopen("nunta.in","r",stdin);
    freopen("nunta.out","w",stdout);
    scanf("%d",&n);
    if(n<3) printf("%d",n);
    else
    {   a[0]=a[1]=b[0] = 1; b[1] = 2;
        for(int i=3;i<=n;++i)
        {   add();
            memcpy(a,b,(b[0]+1)*sizeof(int));
            memcpy(b,c,(c[0]+1)*sizeof(int));
        }
        for(int i=c[0];i;--i) printf("%d",c[i]);
    }
    printf("\n"); return 0;

}