#include<cstdio>
#include<queue>

FILE* in=fopen("barbar.in","r");
FILE* out=fopen("barbar.out","w");

const int Q=1007;

int l,c;

bool d[Q][Q];

struct point{
    int a,b;
};

std::queue<point> q;

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

int sx,sy,fx,fy;

int v[Q][Q];

int viz[Q][Q];

bool ver(int x)
{
    while(!q.empty())
        q.pop();

    q.push(point{sx,sy});

    point act;

    while(!q.empty())
    {
        act=q.front();


        q.pop();

        for(int j=1; j<=4; j++)
        {
            if(d[act.a+dx[j]][act.b+dy[j]]!=1 && v[act.a+dx[j]][act.b+dy[j]]>=x && viz[act.a+dx[j]][act.b+dy[j]]!=x)
            {
                if(act.a+dx[j]==fx && act.b+dy[j]==fy)
                {
                    return 1;
                }

                viz[act.a+dx[j]][act.b+dy[j]]=x;
                q.push(point{act.a+dx[j],act.b+dy[j]});
            }
        }

    }

    return 0;
}

void make()
{
    int nr;
    int pas=0;

    point act;

    while(!q.empty())
    {
        nr=q.size();
        pas++;

        for(int i=1; i<=nr; i++)
        {
            act=q.front();
            q.pop();
            v[act.a][act.b]=pas;

            for(int j=1; j<=4; j++)
            {
                if(d[act.a+dx[j]][act.b+dy[j]]!=1 && v[act.a+dx[j]][act.b+dy[j]]==0)
                    q.push(point{act.a+dx[j],act.b+dy[j]});
            }

        }
    }
}

int main()
{
    fscanf(in,"%d %d\n",&l,&c);

    char h;

    for(int i=1; i<=l; i++)
    {
        d[i][0]=1;
        d[i][c+1]=1;
    }

    for(int j=1; j<=c; j++)
    {
        d[0][j]=1;
        d[l+1][j]=1;
    }

    for(int i=1; i<=l; i++)
    {
        for(int j=1; j<=c; j++)
        {
            fscanf(in,"%c",&h);

            if(h=='*')
                d[i][j]=1;
            if(h=='D')
            {
                q.push(point{i,j});
            }
            if(h=='I')
            {
                sx=i;
                sy=j;
            }
            if(h=='O')
            {
                fx=i;
                fy=j;
            }
        }
        fscanf(in,"\n");
    }

    make();

    int p=1024;

    int k=0;

    while(p)
    {
        if(ver(p+k)==1)
            k+=p;
        p/=2;
    }

    fprintf(out,"%d",k-1);

    return 0;
}