#include<bits/stdc++.h>
using namespace std;
using ll=long long;
int main()
{
    cin.tie(0)->sync_with_stdio(0);
    ll n;cin>>n;
    string s;cin>>s;
    vector<ll>p;
    for(int i=0;i<n;i++)
    {
        if(s[i]=='#')
        {
            p.push_back(i);
        }
    }
    ll ans=-1,mx=0;
    for(int i=0;i<n;i++)
    {
        if(s[i]=='#')continue;
        ll idx=lower_bound(p.begin(),p.end(),i)-p.begin();
        ll d1=1LL<<60,d2=1LL<<60;
        if(idx<p.size())d1=p[idx]-i;
        if(idx>0)d2=i-p[idx-1];
        if(mx<min(d1,d2))
        {
            mx=min(d1,d2);
            ans=i+1;
        }
    }
    assert(ans!=-1);
    cout<<ans<<endl;
}