# codeforces 312 B. Archer

Posted by 111qqz on Tuesday, February 2, 2016

## TOC

##### http://codeforces.com/problemset/problem/312/B

``````/* ***********************************************
Author :111qqz
Created Time :2016年02月02日 星期二 15时57分06秒
File Name :code/cf/518D.cpp
************************************************ */

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <cmath>
#include <cstdlib>
#include <ctime>
#define fst first
#define sec second
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define ms(a,x) memset(a,x,sizeof(a))
typedef long long LL;
#define pi pair < int ,int >
#define MP make_pair

using namespace std;
const double eps = 1E-8;
const int dx4[4]={1,0,0,-1};
const int dy4[4]={0,-1,1,0};
const int inf = 0x3f3f3f3f;
const int N=2E3+7;
int n,t;
double p;
double dp[N][N];
int main()
{
#ifndef  ONLINE_JUDGE
freopen("code/in.txt","r",stdin);
#endif
ms(dp,0);
dp[0][0] = 1;
cin>>n>>p>>t;
for ( int i = 0 ; i <= t ; i++)
{
for ( int j = 0 ; j <= n ; j++)
{
if (j==n)
{
dp[i+1][j]+=dp[i][j];
}
else
{
dp[i+1][j+1]+=dp[i][j]*p;
dp[i+1][j]+=dp[i][j]*(1-p);
}
}
}
double ans = 0 ;
for ( int j = 1 ; j <= n ; j++)
ans +=j*dp[t][j];

printf("%.12f\n",ans);

#ifndef ONLINE_JUDGE
fclose(stdin);
#endif
return 0;
}
``````

「真诚赞赏，手留余香」