#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define all(s) (s).begin(), (s).end()
#define rall(s) (s).rbegin(), (s).rend()
#define rep(i,l,r) for(int i=l;i<r;i++)
#define rrep(i,r,l) for(int i=r;i>=l;i--)

using ll=long long;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int N;cin>>N;
    string S;cin>>S;
    vector<int> left(N),right(N);

    int last=-1;
    rep(i,0,N){
        if(S[i]=='.'){
            if(last==-1)left[i]=1e9;
            else left[i]=i-last;
        }
        else{
            last=i;
        }
    }
    last=-1;
    rrep(i,N-1,0){
        if(S[i]=='.'){
            if(last==-1)right[i]=1e9;
            else right[i]=last-i;
        }
        else last=i;
    }
    int ans=-1;
    int cur=0;
    rep(i,0,N){
        if(S[i]=='#')continue;
        int dist=min(left[i],right[i]);
        if(dist>cur){
            ans=i+1;
            cur=dist;
        }
    }
    cout<<ans<<endl;

}