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11176.cpp
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11176.cpp
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#include <bits/stdc++.h>
using namespace std;
int main(){
int n;
double p;
while (scanf("%d %lf", &n, &p) && n) {
double dp[n + 1][n + 1];
memset(dp, 0, sizeof dp);
dp[0][0] = 1;
for (int i = 0; i < n; i++)
for (int j = 0; j <= n; j++) {
if (abs(dp[i][j]) < 1e-10)
continue;
dp[i + 1][j] += dp[i][j] * (1 - p);
for (int k = 1; k < n - i; k++) {
if (k <= j)
dp[i + k + 1][j] += dp[i][j] * pow(p, k) * (1 - p);
else
dp[i + k + 1][k] += dp[i][j] * pow(p, k) * (1 - p);
}
if (n - i <= j)
dp[n][j] += dp[i][j] * pow(p, n - i);
else
dp[n][n - i] += dp[i][j] * pow(p, n - i);
}
double answer = 0;
for (int i = 0; i <= n; i++)
answer += i * dp[n][i];
printf("%f\n", answer);
}
return 0;
}