518D - Ilya and Escalator - CodeForces Solution

#include<bits/stdc++.h>
using namespace std;
#define int long long
int n, t;
long double p, dp[2500][2500];
signed main(){
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	cout.tie(nullptr);
	cin >> n >> p >> t;
	for (int i = 1; i <= t; i++){
		for (int j = 1; j <= n; j++){
			dp[i][j]=(1-p)*dp[i-1][j]+p*(1+dp[i-1][j-1]);
		} 
	}
	cout << setprecision(6) << fixed << dp[t][n];
}