#include <iostream>
using namespace std;
int fib_n(int n);
int main() {
cout<<"input N"<<endl;
int n;
cin>>n;
cout<<"F:\t"<<fib_n(n)<<endl;
return 0;
}
int fib_n(int n)
{
if (n <= 2) return 1;
int x = 1;
int y = 1;
int ans = 0;
for (int i = 2; i < n; i++)
{
ans = x + y;
x = y;
y = ans;
}
return ans;
}
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