#include <bits/stdc++.h>
#define top() front()
std::ifstream in("barbar.in");std::ofstream out("barbar.out");struct poz{int x,y,cost;};int n,m,x1,x2,y1,y2,viz[1001][1001],viz2[1001][1001];int dx[]={-1,0,1,0};int dy[]={0,1,0,-1};char mat[1001][1001];std::queue<poz>q;bool check(int g){for(int i=1;i<=n;i++)memset(viz2[i],0,sizeof(viz2[i]));if(viz[x1][y1]<g)return 0;q.push({x1,y1,0});while(!q.empty()){poz p=q.top();viz2[p.x][p.y]=1;q.pop();for(int i=0;i<4;i++){poz aux={p.x+dx[i],p.y+dy[i]};if(aux.x>=1 && aux.y>=1 && aux.x<=n && aux.y<=m && viz[aux.x][aux.y]>=g && !viz2[aux.x][aux.y] && mat[aux.x][aux.y]!='*'){viz2[aux.x][aux.y]=1,q.push(aux);if(aux.x==x2 && aux.y==y2){while(!q.empty())q.pop();return 1;}}}}return 0;}int bs(){int p2=1<<20,r=0,ok=0;while(p2){if(check(p2+r))r+=p2,ok=1;p2/=2;}if(!ok)return -1;return r;}int main(){in>>n>>m;for(int i=1;i<=n;i++,in>>std::ws){for(int j=1;j<=m;j++){in>>mat[i][j]>>std::ws;viz[i][j]=INT_MAX;if(mat[i][j]=='D')q.push({i,j,0}),viz[i][j]=0;elseif(mat[i][j]=='I')x1=i,y1=j;elseif(mat[i][j]=='O')x2=i,y2=j;}}while(!q.empty()){poz p=q.top();q.pop();for(int i=0;i<4;i++){poz aux={p.x+dx[i],p.y+dy[i],p.cost+1};if(aux.x>=1 && aux.y>=1 && aux.x<=n && aux.y<=m && mat[aux.x][aux.y]!='*')if(viz[aux.x][aux.y]>aux.cost)viz[aux.x][aux.y]=aux.cost,q.push(aux);}}out<<bs();std::cout<<'\n';return 0;}