#include <bits/stdc++.h>

using namespace std;

int arr[1004][1004];
int aux[1004][1004];
int r, c;

int dx[4] = {-1, 0, 1,  0};
int dy[4] = { 0, 1, 0, -1};

bool OK(int x, int y){
    if(x < 0 || y < 0 || x >= r || y >= c){
        return false;
    }

    if(arr[x][y] == -1 || arr[x][y] >= 1){
        return false;
    }

    return true;
}

bool OK2(int x, int y){
    if(x < 0 || y < 0 || x >= r || y >= c){
        return false;
    }

    if(aux[x][y] == -1 || aux[x][y] > 0){
        return false;
    }

    return true;
}

void construireDrum(int t){
    for(int i = 0; i < r;i++){
        for(int j = 0; j < c; j++){
            if(arr[i][j] - 1 < t && arr[i][j] >= 0){
                aux[i][j] = -1;
            }
            if(arr[i][j] == -1){
                aux[i][j] = -1;
            }
        }
    }
}

void demolareDrum(){
    for(int i = 0; i < r;i++){
        for(int j = 0; j < c; j++){
            aux[i][j] = 0;
        }
    }
}

void lee(queue< pair<int, int> >& coada, int no){

    int x_actual, y_actual, x_urmator, y_urmator;

    while( !coada.empty() ){

        x_actual = coada.front().first;
        y_actual = coada.front().second;
        coada.pop();

        for(int d = 0; d < 4; d++){

            x_urmator = x_actual + dx[d];
            y_urmator = y_actual + dy[d];

            if(no == 1){
                if( OK(x_urmator, y_urmator) ){
                    coada.push( make_pair(x_urmator, y_urmator) );
                    arr[x_urmator][y_urmator] = arr[x_actual][y_actual] + 1;;
                }
            } else {
                if( OK2(x_urmator, y_urmator) ){
                    coada.push( make_pair(x_urmator, y_urmator) );
                    aux[x_urmator][y_urmator] = aux[x_actual][y_actual] + 1;;
                }
            }
        }

    }


}

int main()
{
    ifstream in("barbar.in");
    ofstream out("barbar.out");


    in>>r>>c;
    char ch;
    int sx, sy, fx, fy;

    queue< pair<int, int> > dragoni;

    for(int i = 0; i < r; i++){
        for(int j = 0; j < c; j++){
            in>>ch;
            if(ch == '.'){
                arr[i][j] = 0;
            } else if(ch == '*'){
                arr[i][j] = -1;
            } else if(ch == 'D'){
                arr[i][j] = 1;
                dragoni.push( make_pair(i, j) );
            } else if(ch == 'I'){
                sx = i; sy = j;
            } else {
                fx = i; fy = j;
            }
        }
    }


    lee(dragoni, 1);

    int t = arr[sx][sy];
    bool found = false;

    queue< pair<int, int> > drum;

    while( !found && t > 0){

        construireDrum(t);

        drum.push( make_pair(sx, sy) );
        lee(drum, 2);

        if(aux[fx][fy] > 0){
            found = true;

        } else {
            t--;
            demolareDrum();
        }
    }




    out<<t;

    return 0;
}