#include<bits/stdc++.h>
using namespace std;
int fib(int n , int f[])
{
for(int i =2; i <= n; i++)
{
f[i]=f[i-1]+f[i-2];
}
return f[n];
}
int main()
{
int n;
cin>> n;
int f[n+1];
f[0] = 0;
f[1] = 1;
int ans = fib(n,f);
cout << ans << endl;
return 0;
}
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