#include<stdio.h>
int main()
{
int n;
__int64 s[60];
int i,j;
s[1]=1;
s[2]=2;
for(i=3;i<=50;i++)
s[i]=s[i-1]+s[i-2];
while(scanf("%d",&n)==1)
{
printf("%I64d\n",s[n]);
}
return 0;
}
int main()
{
int n;
__int64 s[60];
int i,j;
s[1]=1;
s[2]=2;
for(i=3;i<=50;i++)
s[i]=s[i-1]+s[i-2];
while(scanf("%d",&n)==1)
{
printf("%I64d\n",s[n]);
}
return 0;
}