#include<stdio.h>
#include<string.h>
#include<queue>

using namespace std;

#define MAXN 1005
#define INF 999999999

int N, M, i, j, X1, Y1, X2, Y2, x, y, xn, yn, st, mid, end, res;
int A[ MAXN ][ MAXN ], B[ MAXN ][ MAXN ], D[ MAXN ][ MAXN ], d[4][2];
char S[ MAXN ];
queue < pair < int, int > > Q;

int main()
{
    FILE *f, *g;

    f = fopen("barbar.in", "r");
    g = fopen("barbar.out", "w");

    fscanf(f, "%d %d", &N, &M);
    fgets(S, 3, f);

    for(i = 0; i <= N + 1; ++i)
        for(j = 0; j <= M + 1; ++j)
            D[i][j] = INF;
    for(i = 0; i <= N+1; ++i)
        A[i][0] = A[i][M+1] = 1;
    for(j = 0; j <= M+1; ++j)
        A[0][j] = A[N+1][j] = 1;

    for(i = 1; i <= N; ++i)
    {
        fgets(S, 1003, f);
        for(j = 0; j < M; ++j)
            if(S[j] == '*')
                A[i][j+1] = 1;
            else if(S[j] == 'D')
                Q.push(make_pair(i, j+1)), D[i][j+1] = 0, A[i][j+1] = 2;
            else if(S[j] == 'I')
                X1 = i, Y1 = j+1;
            else if(S[j] == 'O')
                X2 = i, Y2 = j + 1;
    }

    d[0][0] = 1;
    d[1][0] = -1;
    d[2][1] = 1;
    d[3][1] = -1;
    while(!Q.empty())
    {
        x = Q.front().first;
        y = Q.front().second;
        Q.pop();
        for(i = 0; i < 4; ++i)
        {
            xn = x + d[i][0], yn = y + d[i][1];
            if(D[x][y] + 1 < D[xn][yn] && A[xn][yn] != 1)
                D[xn][yn] = D[x][y] + 1, Q.push(make_pair(xn, yn));
        }
    }

    end = N + M;
    while(st <= end)
    {
        mid = (st + end) / 2;
        memset(B, 0, sizeof(B));
        if(D[X1][Y1] >= mid)
            Q.push(make_pair(X1, Y1)), B[X1][Y1] = 1;
        while(!Q.empty())
        {
            x = Q.front().first;
            y = Q.front().second;
            Q.pop();
            for(i = 0; i < 4; ++i)
            {
                xn = x + d[i][0], yn = y + d[i][1];
                if(!B[xn][yn] && !A[xn][yn] && D[xn][yn] >= mid)
                    B[xn][yn] = 1, Q.push(make_pair(xn, yn));
            }
        }

        if(B[X2][Y2])
            st = mid + 1, res = mid;
        else end = mid - 1;
    }

    fprintf(g, "%d\n", res);

    fclose(f);
    fclose(g);

    return 0;
}