#include <bits/stdc++.h>

typedef long long ll;
typedef unsigned long long ull;

#define FOR(i,a,b) for(int (i)=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define RANGE(vec) (vec).begin(),(vec).end()

using namespace std;


class EvilRecursion {
public:
    void solve(void) {
            int N;
            cin>>N;
            if (N == 0)
            {
                cout<<4<<endl;
                return;
            }
            if (N == 1)
            {
                cout<<3<<endl;
                return;
            }
            vector<long double> dp(N+1,0);
            dp[0] = 4.0;
            dp[1] = 3.0;
            FOR(i, 2, N+1)
                dp[i] = 4.75 *dp[i-1] - 3*dp[i-2];
            cout<<setprecision(20)<<dp[N]<<endl;
    }
};

#if 1
int main(int argc, char *argv[])
{
        ios::sync_with_stdio(false);
        auto obj = new EvilRecursion();
        obj->solve();
        delete obj;
        return 0;
}
#endif