#include <iostream>

using namespace std;

int main()
{
    int n,hol=1,rossz;
    cin>>n;
    string x;
    for(int i=1; i<=n; i++){
        cin>>x;
        if(hol%3!= 0 and hol%5!=0 and x=="BIMM")
            rossz=i+1;
        if(hol%3!= 0 and hol%5!=0 and x=="BUMM")
            rossz=i+1;
        if(hol%3!= 0 and hol%5!=0 and x=="BAMM")
            rossz=i+1;
        if(hol%3!= 0 and hol%5!=0 and x=="BAMM")
            rossz=i+1;
        if(hol%3== 0 and hol%5!=0 and x=="BUMM")
            rossz=i+1;
        if(hol%3== 0 and hol%5!=0 and x=="BAMM")
            rossz=i+1;
        if(hol%3!= 0 and hol%5==0 and x=="BIMM")
            rossz=i+1;
        if(hol%3!= 0 and hol%5==0 and x=="BUMM")
            rossz=i+1;
        if(hol%3== 0 and hol%5==0 and x=="BIMM")
            rossz=i+1;
        if(hol%3== 0 and hol%5==0 and x=="BAMM")
            rossz=i+1;
    }
    cout<<rossz-1;
    return 0;
}