#include <fstream>
using namespace std;
ifstream f("barbar.in");
ofstream g("barbar.out");
int n,R,C,k,xf,yf,xp,yp,maxim;
int d[1011][1011];
int di[4]={-1,0,1,0};
int dj[4]={0,1,0,-1};

struct pozitii{
    int i,j;
};
pozitii h[1011*1011*3],c[1011*1011*4];

void update(){
    int p,c;
    pozitii aux;
    c=k;
    p=c/2;
    while(p>0 && d[h[p].i][h[p].j]>d[h[c].i][h[c].j]){
        aux=h[p],h[p]=h[c],h[c]=aux;
        c=p,p/=2;
    }
}

void stergere(){
    int p=1,c=2;
    pozitii aux=h[1];
    h[1]=h[k],h[k]=aux;
    k--;
    if(c+1<=k && d[h[c].i][h[c].j]>d[h[c+1].i][h[c+1].j]) c++;
  /*  while(c<=k && d[h[p].i][h[p].j]>d[h[c].i][h[c].j]){
        aux=h[p],h[p]=h[c],h[c]=aux;
        p=c,c*=2;
        if(c+1<=k && d[h[c].i][h[c].j]>d[h[c+1].i][h[c+1].j]) c++;
    }*/
}

bool ver(int dist){
    register int i,j,p,u,dr,iv,jv;
    bool viz[1011][1011];
    p=u=1;
    c[p].i=xp,c[p].j=yp;
    if(d[xp][yp]<dist)
        return false;
    while(p<=u){
        for(dr=0;dr<4;dr++){
            iv=c[p].i+di[dr],jv=c[p].j+dj[dr];
            if(iv>0 && jv>0 && jv<=C && iv<=R && !viz[iv][jv]){
                if(d[iv][jv]>=dist)
                    c[++u].i=iv,c[u].j=jv,viz[iv][jv]=true;
                else if(d[iv][jv]==-3)
                    return true;
            }
        }
        p++;
    }
    return false;
}

int main(void){
    register int i,j,x,y,dr,iv,jv;
    char ch;

    f>>R>>C;
    for(i=1;i<=R;i++){
        for(j=1;j<=C;j++){
            f>>ch;
            if(ch=='.')
                d[i][j]=1011*1011*10;
            else if(ch=='*')
                d[i][j]=-1;
            else if(ch=='I')
                d[i][j]=-2,xp=i,yp=j;
            else if(ch=='O')
                d[i][j]=-3,xf=i,yf=j;
            else
                d[i][j]=0,h[++k].i=i,h[k].j=j;
        }
    }

    int nr=0;
    int minim;
    do{
        minim=d[h[1].i][h[1].j];
        x=h[1].i,y=h[1].j;
        stergere();
        for(dr=0;dr<4;dr++){
            iv=x+di[dr],jv=y+dj[dr];
            if(iv>0 && jv>0 && iv<=R && jv<=C){
                if(d[iv][jv]>minim+1)
                    d[iv][jv]=minim+1,h[++k].i=iv,h[k].j=jv,nr++,update();
                else if(d[iv][jv]==-2 || d[iv][jv]==-3){
                    if(maxim<minim)
                        maxim=minim,nr++;
                }
            }
        }
    }while(nr<R*C);

    int p=1,u=maxim,mij,sol;
    while(p<=u){
        mij=p+(u-p)/2;
        if(ver(mij))
            sol=mij,p=mij+1;
        else
         u=mij-1;
    }

    g<<sol;
  /*  for(i=1;i<=R;i++){
        for(j=1;j<=C;j++)
            g<<d[i][j]<<" ";
        g<<"\n";
    }*/

    f.close();
    g.close();
    return 0;
}