#include <iostream>
#include <string>
using namespace std;

int main(){
	int m, t, u, f, d, xp;
	int ansr = 0, anst = 0;
	cin >> m >> t >> u >> f >> d;
	f += f;
	xp = u + d;
	char x;
	for(int i = 1; i <= t && anst <= m; ++i){
		cin >> x;
		if(x == 'u'){
			++ansr;
			anst += xp;
		}
		else if(x == 'f'){
			++ansr;
			anst += f;
		}
		else{
			++ansr;
			anst += xp;
		}
	}
	
	cout << ansr - 1 << endl;
	
	return 0;
}