/*
    "TLE is like the wind, always by my side"
    - Yasuo - 2022 -
*/
#include <bits/stdc++.h>
#define debug(x) cerr << #x << " " << x << "\n"
#define debugs(x) cerr << #x << " " << x << " "

using namespace std;

struct coord
{
    int lin;
    int col;
    int dist;
};

int dlin[5] = {0, 0, 1, -1};
int dcol[5] = {1, -1, 0, 0};
char a[1003][1003];
bool visited[1003][1003];
int distans[1003][1003];
queue<coord> q;
int startl,startc,finl,finc;

bool posibil (int distmin)
{
    int i;
    int l,c;
    coord frontnode;
    q.push({startl,startc,0});
    while (!q.empty())
    {
        frontnode=q.front();
        if (!visited[frontnode.lin][frontnode.col])
        {
            visited[frontnode.lin][frontnode.col]=1;
            for (i=0; i<4; i++)
            {
                l=frontnode.lin;
                c=frontnode.col;
                l+=dlin[i];
                c+=dcol[i];
                if (!visited[l][c] && a[l][c]!='*' && distans[l][c]>=distmin)
                    q.push({l,c,0});
            }
        }
        q.pop();
    }
    if (visited[finl][finc])
        return 1;
    else
        return 0;
}

int main()
{
    ifstream fin("barbar.in");
    ofstream fout("barbar.out");
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int n,m,i,j,l,c,r,pas;
    coord frontnode;
    fin >> n >> m;
    for (i=1; i<=n; i++)
    {
        for (j=1; j<=m; j++)
        {
            fin >> a[i][j];
            if (a[i][j]=='I')
            {
                startl=i;
                startc=j;
            }
            if (a[i][j]=='O')
            {
                finl=i;
                finc=j;
            }
            if (a[i][j]=='D')
                q.push({i,j,0});
        }
    }
    for (i=0; i<=n+1; i++)
    {
        a[i][0]='*';
        a[i][m+1]='*';
    }
    for (i=0; i<=m+1; i++)
    {
        a[0][i]='*';
        a[n+1][i]='*';
    }
    while (!q.empty())
    {
        frontnode=q.front();
        if (!visited[frontnode.lin][frontnode.col])
        {
            visited[frontnode.lin][frontnode.col]=1;
            distans[frontnode.lin][frontnode.col]=frontnode.dist;
            for (i=0; i<4; i++)
            {
                l=frontnode.lin;
                c=frontnode.col;
                l+=dlin[i];
                c+=dcol[i];
                if (!visited[l][c] && a[l][c]!='*')
                    q.push({l,c,frontnode.dist+1});
            }
        }
        q.pop();
    }
    r=0;
    pas=(1<<10);
    while (pas)
    {
        for (i=1;i<=n;i++)
        {
            for (j=1;j<=m;j++)
                 visited[i][j]=0;
        }
        if (posibil(r+pas))
            r+=pas;
        pas=pas/2;
    }
    fout << r;
}