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#include <iostream>
using namespace std;

int fibonacci(int n) {
if (n <= 1) {
return n;
}
int a = 0, b = 1;
for (int i = 2; i <= n; ++i) {
int temp = b;
b = a + b;
a = temp;
}
return b;
}

int main() {
int N;
cin >> N;
cout << fibonacci(N) << endl;
return 0;
}