#include <iostream>
#include <vector>
#include<cmath>

using namespace std;

struct point{
     int x,y;
};

int main(){
    int N,M,diagnum = 0;
    cin >> N >> M;
    double ans = (N+M)*100;
    int num;
    cin >> num;
    vector< point > diag(num);
    for(int i = 0; i < num; ++i){
        cin >> diag[i].x >> diag[i].y;
        --diag[i].x;
        --diag[i].y;
    }
    point CurPos;
    CurPos.x = 0, CurPos.y = 0;
    while(CurPos.x != N && CurPos.y != M){
        bool exists = false;
        int minim = 1e9,minnum;
        for(int i = 0; i < num; ++i){
            if((diag[i].x != -1) && (diag[i].y != -1) && (diag[i].x >= CurPos.x) && (diag[i].y >= CurPos.y)  && ((diag[i].x - CurPos.x + diag[i].y - CurPos.y) < minim)){
                minnum = i;
                minim = diag[i].x - CurPos.x + diag[i].y - CurPos.y;
                exists = true;
            }
        }
        if(exists){
            CurPos.x = diag[minnum].x+1;
            CurPos.y = diag[minnum].y+1;
            diag[minnum].x = diag[minnum].y = - 1;
            ++diagnum;
        }
        else{
            CurPos.x = N;
            CurPos.y = M;
        }
    }
    ans-=diagnum*100*(2 - sqrt(2.0));
    double intpart;
    ans = (modf (ans , &intpart) >= 0.5 ? ceil(ans) : floor(ans));
    cout << ans << endl;
}