#include <iostream>

double exp(const int &i, const int &n, unsigned f = 1) {
    return i == 1
        ? 2 + exp(i + 1, n, f)
        : (i < n
            ? 1.0 / (f * i) + exp(i + 1, n, f * i)
            : 0);
}

int main()
{
    printf("E=%.4f", exp(1, 10));
}

E=2.7183