include<stdio.h>

main()
{int n,m,f1=1,f2=1,f;
scanf("%d",&n);
if(n<3)
{printf("%d",f1);}
else
{for(m=2;m<n;m++)
{f=f1+f2;
f1=f2;
f2=f;}
printf("%d",f);}}