using namespace std;
int m,t,u,f,d,s,ans;
char ch;
int main()
{
cin>>m>>t>>u>>f>>d;
{
for(int i=1;i<=t;i++)
{
cin>>ch;
if(ch=='U'||ch=='D')
{
s=s+u+d;

}
			else if(ch=='F')
			{
				s=s+f*2;
			}
		if(m>=s)
		{
			ans++;
		}
			else 
			{
			
				break;
			}
	}
cout<<ans;
}
}