#include <stdio.h>
#define M1  1005
#define M2  1000005
#define INF 1000000

const int dx[4]={0, 0, -1, 1}, dy[4]={-1, 1, 0, 0};
int minim (int a, int b)
{
    return a<b?a:b;
}

int n, m, i, j, safe[M1][M1], sol[M1][M1], xi, yi, xf, yf, x0, y0, x1, y1, cx[M2], cy[M2], cs, cd;
char t[M1][M1];

int main ()
{
freopen ("barbar.in", "r", stdin);
freopen ("barbar.out", "w", stdout);

scanf ("%d %d\n", &n, &m);
cs = 0;
cd = -1;
for (i=1; i<=n; i++)
{
    for (j=1; j<=m; j++)
    {
        safe[i][j] = INF;
        sol[i][j] = 0;
        scanf ("%c", &t[i][j]);
        if (t[i][j] == 'D')
        {
            safe[i][j] = 0;
            cd++;
            cx[cd] = i;
            cy[cd] = j;
        }
        if (t[i][j] == 'I')
            xi = i;
        yi = j;
        if (t[i][j] == 'O')
            xf = i;
        yf = j;
    }
    scanf ("\n");
}

for (i=0; i<=n+1; i++)
{
    t[i][0] = '*';
    t[i][m+1] = '*';
}

for (i=0; i<=m+1; i++)
{
    t[0][i] = '*';
    t[n+1][i] = '*';
}

while (cs != cd+1)
{
    for (i=0; i<4; i++)
    {
        x0 = cx[cs];
        y0 = cy[cs];
        x1 = x0+dx[i];
        y1 = y0+dy[i];
        if (t[x1][y1] != '*' && safe[x1][y1] > safe[x0][y0]+1)
        {
            safe[x1][y1] = safe[x0][y0]+1;
            cd = (cd+1)%M2;
            cx[cd] = x1;
            cy[cd] = y1;
        }
    }
    cs = (cs+1)%M2;
}

cs = cd = 0;
cx[0] = xi;
cy[0] = yi;
sol[xi][yi] = safe[xi][yi];
while (cs != cd+1)
{
    for (i=0; i<4; i++)
    {
        x0 = cx[cs];
        y0 = cy[cs];
        x1 = x0+dx[i];
        y1 = y0+dy[i];
        if (t[x1][y1] != '*')
        {
            xi = minim(sol[x0][y0], safe[x1][y1]);
            if (sol[x1][y1] < xi)
            {
                sol[x1][y1] = xi;
                cd = (cd+1)%M2;
                cx[cd] = x1;
                cy[cd] = y1;
            }
        }
    }
    cs = (cs+1)%M2;
}

if (sol[xf][yf] > 0)
    printf ("%d\n", sol[xf][yf]);
else
    printf ("-1\n");

return 0;
}