#include <bits/stdc++.h>
#define int long long
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")

using namespace std;
int mat[2005][2005], n, m;
queue<pair<int, int>> q;
pair<int, int> pozi, pozf;
bool ok[2005][2005];

void dfs(pair<int, int> poz, int nivel)
{
    int i = poz.first;
    int j = poz.second;
    //cout<<i<<" "<<j<<" "<<ok[i+1][j]<<" "<<mat[i+1][j]<<'\n';

    ok[i][j]=1;
    if(ok[i+1][j] == 0 && mat[i+1][j]>=nivel && i+1<=n) dfs({i+1, j}, nivel);
    if(ok[i][j+1] == 0 && mat[i][j+1]>=nivel && j+1<=m) dfs({i, j+1}, nivel);
    if(ok[i-1][j] == 0 && mat[i-1][j]>=nivel && i-1>=1) dfs({i-1, j}, nivel);
    if(ok[i][j-1] == 0 && mat[i][j-1]>=nivel && j-1>=1) dfs({i, j-1}, nivel);
}

void reset()
{
    for(int i=1;i<=n;i++)
        for(int j=1;j<=m;j++)
            ok[i][j]=0;
}

void afis(int nivel)
{
    cout<<nivel<<'\n';
    for(int i=1;i<=n;i++){
        for(int j=1;j<=m;j++)
            cout<<ok[i][j];
        cout<<'\n';
    }
    cout<<'\n';
}

bool parcurgere(int nivel)
{
    reset();
    dfs(pozi, nivel);

    //afis(nivel);

    if(ok[pozf.first][pozf.second]==1) return true;
    else return false;
}

int32_t main()
{
    ifstream cin("barbar.in");
    ofstream cout("barbar.out");
    char ch;
    cin>>n>>m;
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            cin>>ch;
            if(ch=='D') mat[i][j]=1, q.push({i, j});
            else if(ch=='*') mat[i][j]=-1;
            else if(ch=='I') pozi = {i, j};
            else if(ch=='O') pozf = {i, j};
            else mat[i][j] = 0;
        }
    }

    while(q.empty()==false)
    {
        int i = q.front().first;
        int j = q.front().second;
        q.pop();
        //cout<<i<<" "<<j<<'\n';
        if(mat[i+1][j]==0 && i+1<=n) mat[i+1][j] = mat[i][j] + 1, q.push({i+1, j});
        if(mat[i][j+1]==0 && j+1<=m) mat[i][j+1] = mat[i][j] + 1, q.push({i, j+1});
        if(mat[i-1][j]==0 && i-1>=1) mat[i-1][j] = mat[i][j] + 1, q.push({i-1, j});
        if(mat[i][j-1]==0 && j-1>=1) mat[i][j-1] = mat[i][j] + 1, q.push({i, j-1});
    }

    int maxx=0;
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
            maxx = max(maxx, mat[i][j]);//, cout<<mat[i][j]<<" ";
        //cout<<'\n';
    }

    int st=1, dr=maxx;
    while(st<=dr)
    {
        int mij=(st+dr)/2;
        //cout<<st<<" "<<dr<<" "<<mij<<'\n';

        if(parcurgere(mij) == true) st = mij + 1;
        else if(parcurgere(mij) == false) dr = mij;
    }
    cout<<(st+dr)/2-1;

    return 0;
}