#include<stdio.h>
#include<string.h>
#define INF 2000000
#define MAXN 1005
FILE *f=fopen("barbar.in","r"), *g=fopen("barbar.out","w");

struct Coordonate{ int x, y; };

int N, M, p=1, u=0;
int A[MAXN][MAXN], viz[MAXN][MAXN];
int Dx[5]={0,-1,0,1,0}, Dy[5]={0,0,1,0,-1};
Coordonate ST, FN, Q[MAXN*MAXN], w;

    // A[][] = INF liber / 0 dragon / -1 obstacol

void Citire(){
int i, j, c;
char s[MAXN];

    fscanf(f,"%d %d\n",&N,&M);

    for(i=1;i<=N;i++){

        fscanf(f,"%s",s);

        for(j=1;j<=M;j++){

            c = s[j-1];

            if( c == '.' )
                A[i][j] = INF;

            else if( c == 'D' ){
                A[i][j] = 0;
                w.x = i;
                w.y = j;
                Q[++u] = w;
            }

            else if( c == '*' )
                A[i][j] = -1;

            else if( c == 'I' ){
                ST.x = i;
                ST.y = j;
                 A[i][j] = INF;
            }

            else if( c == 'O' ){
                FN.x = i;
                FN.y = j;
                 A[i][j] = INF;
            }

        }

    }

    for(i=0;i<=N+1;i++){ A[i][0] = -1; A[i][M+1] = -1; }      // Bordare
    for(j=0;j<=M+1;j++){ A[0][j] = -1; A[N+1][j] = -1; }
/*
    for(int i=0;i<=N+1;i++){

        for(int j=0;j<=M+1;j++){

            if(A[i][j]==-1)
                fprintf(g,"- ");

            else fprintf(g,"%d ",A[i][j]);
        }
        fprintf(g,"\n");
    }
*/
}

void Preprocesare(){
int k, I, J, Inou, Jnou;

    while( p <= u ){

        I = Q[p].x;
        J = Q[p].y;

        for(k=1;k<=4;k++){

            Inou = I + Dx[k];
            Jnou = J + Dy[k];
            w.x = Inou;
            w.y = Jnou;

            if( A[Inou][Jnou] == INF ){
                A[Inou][Jnou] = A[I][J]+1;
                Q[++u] = w;
            }

        }

        p++;
    }

}

int Parcurgere( int LIMITA ){
int k, I, J, Inou, Jnou;

    memset(viz,0,sizeof(viz));

    if( A[ST.x][ST.y] < LIMITA )
        return 0;

    p = 1; u = 1;
    Q[1] = ST;

    while( p <= u ){

        I = Q[p].x;
        J = Q[p].y;

        for(k=1;k<=4;k++){

            Inou = I + Dx[k];
            Jnou = J + Dy[k];
            w.x = Inou;
            w.y = Jnou;

            if( A[Inou][Jnou] != -1 && A[Inou][Jnou] >= LIMITA && viz[Inou][Jnou] == 0 ){

                Q[++u] = w;
                viz[Inou][Jnou] = 1;

                if( Q[u].x == FN.x && Q[u].y == FN.y )
                    return 1;
            }

        }

        p++;
    }
    return 0;
}

void CautareBinara(){
int p = 0, u = N+M-2, mij, sol = -1;

    while( p <= u ){

        mij = (p+u)/2;

        if( Parcurgere(mij) == 1 ){
            p = mij + 1;
            sol = mij;
        }

        else
            u = mij - 1;

    }
    fprintf(g,"%d",sol);

}

int main(){

    Citire();
    Preprocesare();
    CautareBinara();

return 0;
}