#include<iostream>
using namespace std;
#define ll long long
const int MAX = 9e6 + 5;
ll n, fib[MAX];
ll fibb(int n)
{
fib[0] = 0, fib[1] = 1;
for (int i = 2; i <= n; i++)
fib[i] = fib[i - 1] + fib[i - 2];
return fib[n];
}
int main(void)
{
cin >> n;
cout << fibb(n);
//main();
}
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