#include<iostream>
using namespace std;
int Fib(int n)
{
unsigned long long Array[1000000],i;
Array[0]=0;
Array[1]=1;
for(i=2;i<=n-1;)
Array[i]=Array[i-1]+Array[i-2];
cout << Array[n-1];
}
int main ()
{
int n;
cin >> n;
cout << Fib(n);
}
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