#include <bits/stdc++.h>
using namespace std;
 
int process() {
	int previous_result = -1;
	int tosses = 0;
	while(true) {
		int x = rand() % 2;
		++tosses;
		if(previous_result == 1 && x == 1) {
			return tosses;
		}
		previous_result = x;
	}
}
 
int main() {
	const int tries = 8000000;
	double sum = 0;
	for(int rep = 0; rep < tries; ++rep) {
		sum += process();
	}
	printf("%lf\n", sum / tries); // average value
}
 
// N tries -> precision 1/sqrt(N)
// 10^6 -> precision 0.001

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