import sys


def main():
    N = int(sys.stdin.readline().strip())
    f = lambda x: (int(x[0])-1, int(x[1]))
    L = [f(sys.stdin.readline().strip().split()) for x in xrange(N)]
    ans = 0.0
    W = [False] * N
    C = [False] * N
    for s in xrange(N):
        if W[s]:
            continue
        v = s
        while not W[v]:
            W[v] = True
            v = L[v][0]
        if C[v]:
            continue
        u = v
        h = 1.0
        while not C[u]:
            C[u] = True
            h *= L[u][1] * 0.01
            u = L[u][0]
        if v == u:
            ans += h
    print '%.2f' % (ans,)


if __name__ == '__main__':
    main()