为什么会RE啊！！！

#include <bits/stdc++.h>
#define N 100005
using namespace std;
long double f[N];

int main () {
    int n;
 	cin >> n;
	f[1] = 0;
	double cnt;
 	for (int i = 1;i <= n;i++) {
        char c;
        cin >> c;
		if(c == 'o') {
			f[i] = f[i - 1] - cnt * cnt + (cnt + 1.0) * (cnt + 1.0);
			cnt++;
		} else if(c == 'x'){
			cnt = 0.0;
            f[i] = f[i -  1];
		} else if(c == '?') {
			f[i] = (f[i - 1] - cnt * cnt + (cnt + 1.0) * (cnt + 1.0) + f[i -  1]) / 2.0;
			cnt = (cnt + 1) / 2;
		}
	}
	printf("%.4Lf" , f[n]);
	return 0;
}

90分记录