#include <bits/stdc++.h>

using namespace std;

ifstream in("barbar.in");
ofstream out("barbar.out");

const int N=1005,M=16;

int dx[]= {-1,0,1,0};
int dy[]= {0,-1,0,1};

struct poz
{
    int x;
    int y;
};

char a[N][N];

bool f[N][N];

int b[N][N],n,m;

poz start,stop,aux;

queue <poz> q;

void read()
{
    in>>n>>m;
    for(int i=1; i<=n; ++i)
        {
        for(int j=1; j<=m; ++j)
            {
            in>>a[i][j];
            if(a[i][j]=='I')
                {
                start.x=i;
                start.y=j;
                }
            else if(a[i][j]=='O')
                {
                stop.x=i;
                stop.y=j;
                }
            else if(a[i][j]=='D')
                {
                aux.x=i;
                aux.y=j;
                q.push(aux);
                b[i][j]=1;
                }
            }
        }
}

void border()
{
    for(int i=0; i<=n+1; ++i)
        {
        a[i][0]=a[i][n+1]='*';
        }
    for(int j=0; j<=m+1; ++j)
        {
        a[0][j]=a[n+1][j]='*';
        }
}

void lee()
{
    border();
    poz k1,k2;
    while(!q.empty())
        {
        k1=q.front();
        q.pop();
        for(int i=0; i<4; ++i)
            {
            k2.x=k1.x+dx[i];
            k2.y=k1.y+dy[i];
            if(a[k2.x][k2.y]!='*')
                {
                if(b[k2.x][k2.y]==0)
                    {
                        q.push(k2);
                        b[k2.x][k2.y]=b[k1.x][k1.y]+1;
                    }
                }
            }
        }
}

bool check(int t)
{
    if(b[start.x][start.y]<t)
        {
        return false;
        }
    for(int i=0;i<=n+1;++i)
        for(int j=0;j<=m+1;++j)
            f[i][j]=0;
    while(!q.empty())
        {
        q.pop();
        }
    poz k1,k2;
    q.push(start);
    f[start.x][start.y]=1;
    while(!q.empty())
        {
        k1=q.front();
        q.pop();
        for(int i=0; i<4; ++i)
            {
            k2.x=k1.x+dx[i];
            k2.y=k1.y+dy[i];
            if(b[k1.x][k1.y]>t&&a[k2.x][k2.y]!='*'&&f[k2.x][k2.y]!=1)
                {
                if(k2.x==stop.x&&k2.y==stop.y)
                    {
                    return true;
                    }
                f[k2.x][k2.y]=1;
                q.push(k2);
                }
            }
        }
    return false;
}

int binarySearch()
{
    int ans=0;
    int pas=1<<M;
    while(pas>0)
        {
        if(check(ans+pas))
            ans+=pas;
        pas/=2;
        }
    return ans;
}

int main()
{
    read();
    /*while(!q.empty())
        {
        out<<q.front().x<<" "<<q.front().y<<'\n';
        q.pop();
        }*/
    lee();
    out<<binarySearch();
    return 0;
}