import sys
input = sys.stdin.readline
n = int(input())
dp = [0]*46
dp[1] = 1
for i in range(2,n+1):
dp[i] = dp[i-1] + dp[i-2]
print(dp[n])
#include <stdio.h>
int main(void) {
int n;
int a=0;
int b=1;
int c;
scanf("%d", &n);
if(n==0){
printf("0");
}
else if(n==1){
printf("1");
}
else{
for(int i=1;i<n;i++){
c= a+b;
a= b;
b= c;
}
printf("%d", c);
}
return 0;
}