#include <fstream>

using namespace std;

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

const int N=1000;
const int dl[]= {-1,0,1,0};
const int dc[]= {0,-1,0,1};

struct punct
{
    int l,c;
};

punct x,y,xi,xf,q[N*N];

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

bool exista_drum(int d)
{
    int st=0,dr=-1;
    if (a[xi.l][xi.c] < d)
    {
        return false;
    }
    for (int i = 1; i <= n; i++)
    {
        for (int j = 1; j <= n; j++)
        {
            b[i][j] = false;
        }
    }
    q[++dr] = xi;
    while(st<=dr)
    {
        x=q[st++];
        for(int i=0; i<4; i++)
        {
            y.l=x.l+dl[i];
            y.c=x.c+dc[i];
            if(a[y.l][y.c] >= d && !b[y.l][y.c])
            {
                q[++dr]=y;
                b[y.l][y.c] = true;
            }
        }
    }
    return b[xf.l][xf.c];
}

int main()
{

    char lin[1000];
    in>>n>>m;
    int st=0,dr=-1;
    for(int i=0; i<=n+1; i++)
        a[i][0]=-2,a[i][m+1]=-2;
    for(int j=0;j<=m+1;j++)
        a[0][j]=-2,a[n+1][j]=-2;
    for(int i=1; i<=n; i++)
    {
        in>>(lin+1);
        for(int j=1; j<=m; j++)
        {

            if(lin[j]=='.')
                a[i][j]=-1;
            else if(lin[j]=='*')
                a[i][j]=-2;

            else if(lin[j]=='I')
                a[i][j]=-1,xi=(punct)
            {
                i,j
            };
            else if(lin[j]=='O')
                a[i][j]=-1,xf=(punct)
            {
                i,j
            };
            else
            {
                q[++dr]=(punct)
                {
                    i,j
                };
                a[i][j]=0;
            }
        }
    }
    while(st<=dr)
    {
        x=q[st++];
        for(int i=0; i<4; i++)
        {
            y.l=x.l+dl[i];
            y.c=x.c+dc[i];
            if(a[y.l][y.c]==-1)
            {
                q[++dr]=y;
                a[y.l][y.c]=1+a[x.l][x.c];
            }
        }
    }
    st=0,dr=2000;
    while(st<dr)
    {
        int mij=(st+dr)/2;
        if(exista_drum(mij))
            st=mij+1;
        else dr=mij;
    }
    /*
    for(int i=1; i<=n; i++)
    {
        for(int j=1; j<=n; j++)
            out<<a[i][j]<<" ";
        out<<"\n";
    }
    */
    out << st - 1;
    return 0;
}